Fix incorrect error messages in the client stack and use ?? for null checks where appropriate

src/OpenIddict.Abstractions/OpenIddictResources.resx

@@ -1197,6 +1197,14 @@ To apply redirection responses, create a class implementing 'IOpenIddictClientHa
   <data name="ID0311" xml:space="preserve">
     <value>A refresh token must be specified when using the refresh token grant.</value>
   </data>
+  <data name="ID0312" xml:space="preserve">
+    <value>The event handler of type '{0}' couldn't be resolved.
+This may indicate that it was not properly registered in the dependency injection container. To register an event handler, use 'services.AddOpenIddict().AddClient().AddEventHandler()'.</value>
+  </data>
+  <data name="ID0313" xml:space="preserve">
+    <value>A discovery client must be registered when using server discovery.
+Reference the 'OpenIddict.Client.SystemNetHttp' package and call 'services.AddOpenIddict().AddClient().UseSystemNetHttp()' to register the default System.Net.Http-based integration.</value>
+  </data>
   <data name="ID2000" xml:space="preserve">
     <value>The security token is missing.</value>
   </data>

src/OpenIddict.Client.AspNetCore/OpenIddictClientAspNetCoreHandlers.cs

@@ -698,7 +698,7 @@ public static partial class OpenIddictClientAspNetCoreHandlers
             // If it was not registered or enabled, let the default OpenIddict client handlers render
             // a default error page instead of delegating the rendering to the status code middleware.
             var feature = response.HttpContext.Features.Get<IStatusCodePagesFeature>();
-            if (feature is null || !feature.Enabled)
+            if (feature is not { Enabled: true })
             {
                 return default;
             }

src/OpenIddict.Client.SystemNetHttp/OpenIddictClientSystemNetHttpHandlers.cs

@@ -222,21 +222,15 @@ public static partial class OpenIddictClientSystemNetHttpHandlers
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0173));
 
             var assembly = typeof(OpenIddictClientSystemNetHttpOptions).Assembly.GetName();
-            using var client = _factory.CreateClient(assembly.Name!);
-            if (client is null)
-            {
+            using var client = _factory.CreateClient(assembly.Name!) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0174));
-            }
 
 #if SUPPORTS_HTTP_CLIENT_DEFAULT_REQUEST_VERSION
             // If supported, import the HTTP version from the client instance.
             request.Version = client.DefaultRequestVersion;
 #endif
-            var response = await client.SendAsync(request, HttpCompletionOption.ResponseContentRead);
-            if (response is null)
-            {
+            var response = await client.SendAsync(request, HttpCompletionOption.ResponseContentRead) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0175));
-            }
 
             // Store the HttpResponseMessage in the transaction properties.
             context.Transaction.SetProperty(typeof(HttpResponseMessage).FullName!, response);

src/OpenIddict.Client/OpenIddictClientBuilder.cs

@@ -372,11 +372,8 @@ public class OpenIddictClientBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0062), nameof(resource));
         }
 
-        using var stream = assembly.GetManifestResourceStream(resource);
-        if (stream is null)
-        {
+        using var stream = assembly.GetManifestResourceStream(resource) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0064));
-        }
 
         return AddEncryptionCertificate(stream, password, flags);
     }
@@ -429,13 +426,10 @@ public class OpenIddictClientBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0065), nameof(thumbprint));
         }
 
-        var certificate = GetCertificate(StoreLocation.CurrentUser, thumbprint) ?? GetCertificate(StoreLocation.LocalMachine, thumbprint);
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddEncryptionCertificate(certificate);
+        return AddEncryptionCertificate(
+            GetCertificate(StoreLocation.CurrentUser, thumbprint)  ??
+            GetCertificate(StoreLocation.LocalMachine, thumbprint) ??
+            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
 
         static X509Certificate2? GetCertificate(StoreLocation location, string thumbprint)
         {
@@ -465,16 +459,10 @@ public class OpenIddictClientBuilder
         using var store = new X509Store(name, location);
         store.Open(OpenFlags.ReadOnly);
 
-        var certificate = store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
-            .OfType<X509Certificate2>()
-            .SingleOrDefault();
-
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddEncryptionCertificate(certificate);
+        return AddEncryptionCertificate(
+            store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
+                .OfType<X509Certificate2>()
+                .SingleOrDefault() ?? throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
     }
 
     /// <summary>
@@ -780,11 +768,8 @@ public class OpenIddictClientBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0062), nameof(resource));
         }
 
-        using var stream = assembly.GetManifestResourceStream(resource);
-        if (stream is null)
-        {
+        using var stream = assembly.GetManifestResourceStream(resource) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0064));
-        }
 
         return AddSigningCertificate(stream, password, flags);
     }
@@ -837,13 +822,10 @@ public class OpenIddictClientBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0065), nameof(thumbprint));
         }
 
-        var certificate = GetCertificate(StoreLocation.CurrentUser, thumbprint) ?? GetCertificate(StoreLocation.LocalMachine, thumbprint);
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddSigningCertificate(certificate);
+        return AddSigningCertificate(
+            GetCertificate(StoreLocation.CurrentUser, thumbprint)  ??
+            GetCertificate(StoreLocation.LocalMachine, thumbprint) ??
+            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
 
         static X509Certificate2? GetCertificate(StoreLocation location, string thumbprint)
         {
@@ -873,16 +855,10 @@ public class OpenIddictClientBuilder
         using var store = new X509Store(name, location);
         store.Open(OpenFlags.ReadOnly);
 
-        var certificate = store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
-            .OfType<X509Certificate2>()
-            .SingleOrDefault();
-
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddSigningCertificate(certificate);
+        return AddSigningCertificate(
+            store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
+                .OfType<X509Certificate2>()
+                .SingleOrDefault() ?? throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
     }
 
     /// <summary>

src/OpenIddict.Client/OpenIddictClientConfiguration.cs

@@ -49,7 +49,7 @@ public class OpenIddictClientConfiguration : IPostConfigureOptions<OpenIddictCli
                     if (!options.Handlers.Any(descriptor => descriptor.ContextType == typeof(ApplyConfigurationRequestContext)) ||
                         !options.Handlers.Any(descriptor => descriptor.ContextType == typeof(ApplyCryptographyRequestContext)))
                     {
-                        throw new InvalidOperationException(SR.GetResourceString(SR.ID0135));
+                        throw new InvalidOperationException(SR.GetResourceString(SR.ID0313));
                     }
 
                     if (registration.MetadataAddress is null)

src/OpenIddict.Client/OpenIddictClientDispatcher.cs

@@ -93,16 +93,15 @@ public class OpenIddictClientDispatcher : IOpenIddictClientDispatcher
                     continue;
                 }
 
-                var handler = descriptor.ServiceDescriptor.ImplementationInstance is not null ?
-                    descriptor.ServiceDescriptor.ImplementationInstance as IOpenIddictClientHandler<TContext> :
-                    _provider.GetService(descriptor.ServiceDescriptor.ServiceType) as IOpenIddictClientHandler<TContext>;
-
-                if (handler is null)
+                yield return descriptor.ServiceDescriptor switch
                 {
-                    throw new InvalidOperationException(SR.FormatID0138(descriptor.ServiceDescriptor.ServiceType));
-                }
+                    { ImplementationInstance: IOpenIddictClientHandler<TContext> handler } => handler,
+
+                    _ when _provider.GetService(descriptor.ServiceDescriptor.ServiceType)
+                        is IOpenIddictClientHandler<TContext> handler => handler,
 
-                yield return handler;
+                    _ => throw new InvalidOperationException(SR.FormatID0312(descriptor.ServiceDescriptor.ServiceType))
+                };
             }
         }
 

src/OpenIddict.Client/OpenIddictClientHandlers.cs

@@ -362,11 +362,8 @@ public static partial class OpenIddictClientHandlers
             // Note: if the static registration cannot be found in the options, this may indicate
             // the client was removed after the authorization dance started and thus, can no longer
             // be used to authenticate users. In this case, throw an exception to abort the flow.
-            var registration = context.Options.Registrations.Find(registration => registration.Issuer == issuer);
-            if (registration is null)
-            {
+            var registration = context.Options.Registrations.Find(registration => registration.Issuer == issuer) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0292));
-            }
 
             context.Issuer = issuer;
             context.Registration = registration;
@@ -1096,11 +1093,7 @@ public static partial class OpenIddictClientHandlers
 
             // Resolve the hash algorithm corresponding to the signing algorithm. If an
             // instance of the BCL hash algorithm cannot be resolved, throw an exception.
-            var algorithm = GetHashAlgorithm(name);
-            if (algorithm is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0293));
-            }
+            var algorithm = GetHashAlgorithm(name) ?? throw new InvalidOperationException(SR.GetResourceString(SR.ID0293));
 
             // If a frontchannel access token was returned in the authorization response,
             // ensure the at_hash claim matches the hash of the actual access token.
@@ -1988,11 +1981,7 @@ public static partial class OpenIddictClientHandlers
 
             // Resolve the hash algorithm corresponding to the signing algorithm. If an
             // instance of the BCL hash algorithm cannot be resolved, throw an exception.
-            var algorithm = GetHashAlgorithm(name);
-            if (algorithm is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0295));
-            }
+            var algorithm = GetHashAlgorithm(name) ?? throw new InvalidOperationException(SR.GetResourceString(SR.ID0295));
 
             var hash = context.BackchannelIdentityTokenPrincipal.GetClaim(Claims.AccessTokenHash);
             if (string.IsNullOrEmpty(hash))
@@ -2404,7 +2393,8 @@ public static partial class OpenIddictClientHandlers
         /// <inheritdoc/>
         public async ValueTask HandleAsync(ProcessAuthenticationContext context!!)
         {
-            if (context.UserinfoTokenPrincipal is not null || string.IsNullOrEmpty(context.UserinfoToken))
+            if (context.UserinfoTokenPrincipal is not null ||
+                string.IsNullOrEmpty(context.UserinfoToken))
             {
                 return;
             }

src/OpenIddict.Client/OpenIddictClientService.cs

@@ -55,13 +55,8 @@ public class OpenIddictClientService
             request = await ApplyConfigurationRequestAsync();
             var response = await ExtractConfigurationResponseAsync();
 
-            var configuration = await HandleConfigurationResponseAsync();
-            if (configuration is null)
-            {
+            return await HandleConfigurationResponseAsync() ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0145));
-            }
-
-            return configuration;
 
             async ValueTask<OpenIddictRequest> PrepareConfigurationRequestAsync()
             {
@@ -195,13 +190,8 @@ public class OpenIddictClientService
 
             var response = await ExtractCryptographyResponseAsync();
 
-            var keys = await HandleCryptographyResponseAsync();
-            if (keys is null)
-            {
+            return await HandleCryptographyResponseAsync() ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0147));
-            }
-
-            return keys;
 
             async ValueTask<OpenIddictRequest> PrepareCryptographyRequestAsync()
             {

src/OpenIddict.Core/Caches/OpenIddictApplicationCache.cs

@@ -272,13 +272,8 @@ public class OpenIddictApplicationCache<TApplication> : IOpenIddictApplicationCa
 
         if (application is not null)
         {
-            var signal = await CreateExpirationSignalAsync(application, cancellationToken);
-            if (signal is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197));
-            }
-
-            entry.AddExpirationToken(signal);
+            entry.AddExpirationToken(await CreateExpirationSignalAsync(application, cancellationToken) ??
+                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197)));
         }
 
         entry.SetSize(1L);
@@ -299,13 +294,8 @@ public class OpenIddictApplicationCache<TApplication> : IOpenIddictApplicationCa
 
         foreach (var application in applications)
         {
-            var signal = await CreateExpirationSignalAsync(application, cancellationToken);
-            if (signal is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197));
-            }
-
-            entry.AddExpirationToken(signal);
+            entry.AddExpirationToken(await CreateExpirationSignalAsync(application, cancellationToken) ??
+                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197)));
         }
 
         entry.SetSize(applications.Length);

src/OpenIddict.Core/Caches/OpenIddictAuthorizationCache.cs

@@ -448,13 +448,8 @@ public class OpenIddictAuthorizationCache<TAuthorization> : IOpenIddictAuthoriza
 
         if (authorization is not null)
         {
-            var signal = await CreateExpirationSignalAsync(authorization, cancellationToken);
-            if (signal is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197));
-            }
-
-            entry.AddExpirationToken(signal);
+            entry.AddExpirationToken(await CreateExpirationSignalAsync(authorization, cancellationToken) ??
+                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197)));
         }
 
         entry.SetSize(1L);
@@ -475,13 +470,8 @@ public class OpenIddictAuthorizationCache<TAuthorization> : IOpenIddictAuthoriza
 
         foreach (var authorization in authorizations)
         {
-            var signal = await CreateExpirationSignalAsync(authorization, cancellationToken);
-            if (signal is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197));
-            }
-
-            entry.AddExpirationToken(signal);
+            entry.AddExpirationToken(await CreateExpirationSignalAsync(authorization, cancellationToken) ??
+                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197)));
         }
 
         entry.SetSize(authorizations.Length);

src/OpenIddict.Core/Caches/OpenIddictScopeCache.cs

@@ -245,13 +245,8 @@ public class OpenIddictScopeCache<TScope> : IOpenIddictScopeCache<TScope>, IDisp
 
         if (scope is not null)
         {
-            var signal = await CreateExpirationSignalAsync(scope, cancellationToken);
-            if (signal is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197));
-            }
-
-            entry.AddExpirationToken(signal);
+            entry.AddExpirationToken(await CreateExpirationSignalAsync(scope, cancellationToken) ??
+                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197)));
         }
 
         entry.SetSize(1L);
@@ -272,13 +267,8 @@ public class OpenIddictScopeCache<TScope> : IOpenIddictScopeCache<TScope>, IDisp
 
         foreach (var scope in scopes)
         {
-            var signal = await CreateExpirationSignalAsync(scope, cancellationToken);
-            if (signal is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197));
-            }
-
-            entry.AddExpirationToken(signal);
+            entry.AddExpirationToken(await CreateExpirationSignalAsync(scope, cancellationToken) ??
+                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197)));
         }
 
         entry.SetSize(scopes.Length);

src/OpenIddict.Core/Caches/OpenIddictTokenCache.cs

@@ -500,13 +500,8 @@ public class OpenIddictTokenCache<TToken> : IOpenIddictTokenCache<TToken>, IDisp
 
         if (token is not null)
         {
-            var signal = await CreateExpirationSignalAsync(token, cancellationToken);
-            if (signal is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197));
-            }
-
-            entry.AddExpirationToken(signal);
+            entry.AddExpirationToken(await CreateExpirationSignalAsync(token, cancellationToken) ??
+                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197)));
         }
 
         entry.SetSize(1L);
@@ -527,13 +522,8 @@ public class OpenIddictTokenCache<TToken> : IOpenIddictTokenCache<TToken>, IDisp
 
         foreach (var token in tokens)
         {
-            var signal = await CreateExpirationSignalAsync(token, cancellationToken);
-            if (signal is null)
-            {
-                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197));
-            }
-
-            entry.AddExpirationToken(signal);
+            entry.AddExpirationToken(await CreateExpirationSignalAsync(token, cancellationToken) ??
+                throw new InvalidOperationException(SR.GetResourceString(SR.ID0197)));
         }
 
         entry.SetSize(tokens.Length);

src/OpenIddict.Core/Managers/OpenIddictApplicationManager.cs

@@ -191,11 +191,8 @@ public class OpenIddictApplicationManager<TApplication> : IOpenIddictApplication
     public virtual async ValueTask<TApplication> CreateAsync(
         OpenIddictApplicationDescriptor descriptor!!, CancellationToken cancellationToken = default)
     {
-        var application = await Store.InstantiateAsync(cancellationToken);
-        if (application is null)
-        {
+        var application = await Store.InstantiateAsync(cancellationToken) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0208));
-        }
 
         await PopulateAsync(application, descriptor, cancellationToken);
 

src/OpenIddict.Core/Managers/OpenIddictAuthorizationManager.cs

@@ -147,11 +147,8 @@ public class OpenIddictAuthorizationManager<TAuthorization> : IOpenIddictAuthori
     public virtual async ValueTask<TAuthorization> CreateAsync(
         OpenIddictAuthorizationDescriptor descriptor!!, CancellationToken cancellationToken = default)
     {
-        var authorization = await Store.InstantiateAsync(cancellationToken);
-        if (authorization is null)
-        {
+        var authorization = await Store.InstantiateAsync(cancellationToken) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0220));
-        }
 
         await PopulateAsync(authorization, descriptor, cancellationToken);
         await CreateAsync(authorization, cancellationToken);

src/OpenIddict.Core/Managers/OpenIddictScopeManager.cs

@@ -140,11 +140,8 @@ public class OpenIddictScopeManager<TScope> : IOpenIddictScopeManager where TSco
     public virtual async ValueTask<TScope> CreateAsync(
         OpenIddictScopeDescriptor descriptor!!, CancellationToken cancellationToken = default)
     {
-        var scope = await Store.InstantiateAsync(cancellationToken);
-        if (scope is null)
-        {
+        var scope = await Store.InstantiateAsync(cancellationToken) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0223));
-        }
 
         await PopulateAsync(scope, descriptor, cancellationToken);
         await CreateAsync(scope, cancellationToken);

src/OpenIddict.Core/Managers/OpenIddictTokenManager.cs

@@ -155,11 +155,8 @@ public class OpenIddictTokenManager<TToken> : IOpenIddictTokenManager where TTok
     public virtual async ValueTask<TToken> CreateAsync(
         OpenIddictTokenDescriptor descriptor!!, CancellationToken cancellationToken = default)
     {
-        var token = await Store.InstantiateAsync(cancellationToken);
-        if (token is null)
-        {
+        var token = await Store.InstantiateAsync(cancellationToken) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0226));
-        }
 
         await PopulateAsync(token, descriptor, cancellationToken);
         await CreateAsync(token, cancellationToken);

src/OpenIddict.Core/OpenIddictCoreBuilder.cs

@@ -66,11 +66,8 @@ public class OpenIddictCoreBuilder
     /// <returns>The <see cref="OpenIddictCoreBuilder"/>.</returns>
     public OpenIddictCoreBuilder AddApplicationStore(Type type!!, ServiceLifetime lifetime = ServiceLifetime.Scoped)
     {
-        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(IOpenIddictApplicationStore<>));
-        if (root is null)
-        {
+        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(IOpenIddictApplicationStore<>)) ??
             throw new ArgumentException(SR.GetResourceString(SR.ID0232), nameof(type));
-        }
 
         // Note: managers can be either open generics (e.g OpenIddictApplicationStore<>)
         // or closed generics (e.g OpenIddictApplicationStore<OpenIddictApplication>).
@@ -117,11 +114,8 @@ public class OpenIddictCoreBuilder
     /// <returns>The <see cref="OpenIddictCoreBuilder"/>.</returns>
     public OpenIddictCoreBuilder AddAuthorizationStore(Type type!!, ServiceLifetime lifetime = ServiceLifetime.Scoped)
     {
-        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(IOpenIddictAuthorizationStore<>));
-        if (root is null)
-        {
+        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(IOpenIddictAuthorizationStore<>)) ??
             throw new ArgumentException(SR.GetResourceString(SR.ID0232), nameof(type));
-        }
 
         // Note: managers can be either open generics (e.g OpenIddictAuthorizationStore<>)
         // or closed generics (e.g OpenIddictAuthorizationStore<OpenIddictAuthorization>).
@@ -168,11 +162,8 @@ public class OpenIddictCoreBuilder
     /// <returns>The <see cref="OpenIddictCoreBuilder"/>.</returns>
     public OpenIddictCoreBuilder AddScopeStore(Type type!!, ServiceLifetime lifetime = ServiceLifetime.Scoped)
     {
-        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(IOpenIddictScopeStore<>));
-        if (root is null)
-        {
+        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(IOpenIddictScopeStore<>)) ??
             throw new ArgumentException(SR.GetResourceString(SR.ID0232), nameof(type));
-        }
 
         // Note: managers can be either open generics (e.g OpenIddictScopeStore<>)
         // or closed generics (e.g OpenIddictScopeStore<OpenIddictScope>).
@@ -219,11 +210,8 @@ public class OpenIddictCoreBuilder
     /// <returns>The <see cref="OpenIddictCoreBuilder"/>.</returns>
     public OpenIddictCoreBuilder AddTokenStore(Type type!!, ServiceLifetime lifetime = ServiceLifetime.Scoped)
     {
-        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(IOpenIddictTokenStore<>));
-        if (root is null)
-        {
+        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(IOpenIddictTokenStore<>)) ??
             throw new ArgumentException(SR.GetResourceString(SR.ID0232), nameof(type));
-        }
 
         // Note: managers can be either open generics (e.g OpenIddictTokenStore<>)
         // or closed generics (e.g OpenIddictTokenStore<OpenIddictToken>).
@@ -268,11 +256,8 @@ public class OpenIddictCoreBuilder
     /// <returns>The <see cref="OpenIddictCoreBuilder"/>.</returns>
     public OpenIddictCoreBuilder ReplaceApplicationManager(Type type!!)
     {
-        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(OpenIddictApplicationManager<>));
-        if (root is null)
-        {
+        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(OpenIddictApplicationManager<>)) ??
             throw new ArgumentException(SR.GetResourceString(SR.ID0232), nameof(type));
-        }
 
         // Note: managers can be either open generics (e.g OpenIddictApplicationManager<>)
         // or closed generics (e.g OpenIddictApplicationManager<OpenIddictApplication>).
@@ -352,11 +337,8 @@ public class OpenIddictCoreBuilder
     /// <returns>The <see cref="OpenIddictCoreBuilder"/>.</returns>
     public OpenIddictCoreBuilder ReplaceAuthorizationManager(Type type!!)
     {
-        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(OpenIddictAuthorizationManager<>));
-        if (root is null)
-        {
+        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(OpenIddictAuthorizationManager<>)) ??
             throw new ArgumentException(SR.GetResourceString(SR.ID0232), nameof(type));
-        }
 
         // Note: managers can be either open generics (e.g OpenIddictAuthorizationManager<>)
         // or closed generics (e.g OpenIddictAuthorizationManager<OpenIddictAuthorization>).
@@ -436,11 +418,8 @@ public class OpenIddictCoreBuilder
     /// <returns>The <see cref="OpenIddictCoreBuilder"/>.</returns>
     public OpenIddictCoreBuilder ReplaceScopeManager(Type type!!)
     {
-        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(OpenIddictScopeManager<>));
-        if (root is null)
-        {
+        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(OpenIddictScopeManager<>)) ??
             throw new ArgumentException(SR.GetResourceString(SR.ID0232), nameof(type));
-        }
 
         // Note: managers can be either open generics (e.g OpenIddictScopeManager<>)
         // or closed generics (e.g OpenIddictScopeManager<OpenIddictScope>).
@@ -520,11 +499,8 @@ public class OpenIddictCoreBuilder
     /// <returns>The <see cref="OpenIddictCoreBuilder"/>.</returns>
     public OpenIddictCoreBuilder ReplaceTokenManager(Type type!!)
     {
-        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(OpenIddictTokenManager<>));
-        if (root is null)
-        {
+        var root = OpenIddictHelpers.FindGenericBaseType(type, typeof(OpenIddictTokenManager<>)) ??
             throw new ArgumentException(SR.GetResourceString(SR.ID0232), nameof(type));
-        }
 
         // Note: managers can be either open generics (e.g OpenIddictTokenManager<>)
         // or closed generics (e.g OpenIddictTokenManager<OpenIddictToken>).

src/OpenIddict.Core/OpenIddictCoreExtensions.cs

@@ -43,52 +43,44 @@ public static class OpenIddictCoreExtensions
         builder.Services.TryAddScoped<IOpenIddictScopeStoreResolver, OpenIddictScopeStoreResolver>();
         builder.Services.TryAddScoped<IOpenIddictTokenStoreResolver, OpenIddictTokenStoreResolver>();
 
-        builder.Services.TryAddScoped(provider =>
+        builder.Services.TryAddScoped(static provider =>
         {
-            var options = provider.GetRequiredService<IOptionsMonitor<OpenIddictCoreOptions>>().CurrentValue;
-            if (options.DefaultApplicationType is null)
-            {
+            var type = provider.GetRequiredService<IOptionsMonitor<OpenIddictCoreOptions>>()
+                .CurrentValue?.DefaultApplicationType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0273));
-            }
 
             return (IOpenIddictApplicationManager) provider.GetRequiredService(
-                typeof(OpenIddictApplicationManager<>).MakeGenericType(options.DefaultApplicationType));
+                typeof(OpenIddictApplicationManager<>).MakeGenericType(type));
         });
 
-        builder.Services.TryAddScoped(provider =>
+        builder.Services.TryAddScoped(static provider =>
         {
-            var options = provider.GetRequiredService<IOptionsMonitor<OpenIddictCoreOptions>>().CurrentValue;
-            if (options.DefaultAuthorizationType is null)
-            {
+            var type = provider.GetRequiredService<IOptionsMonitor<OpenIddictCoreOptions>>()
+                .CurrentValue?.DefaultAuthorizationType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0274));
-            }
 
             return (IOpenIddictAuthorizationManager) provider.GetRequiredService(
-                typeof(OpenIddictAuthorizationManager<>).MakeGenericType(options.DefaultAuthorizationType));
+                typeof(OpenIddictAuthorizationManager<>).MakeGenericType(type));
         });
 
-        builder.Services.TryAddScoped(provider =>
+        builder.Services.TryAddScoped(static provider =>
         {
-            var options = provider.GetRequiredService<IOptionsMonitor<OpenIddictCoreOptions>>().CurrentValue;
-            if (options.DefaultScopeType is null)
-            {
+            var type = provider.GetRequiredService<IOptionsMonitor<OpenIddictCoreOptions>>()
+                .CurrentValue?.DefaultScopeType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0275));
-            }
 
             return (IOpenIddictScopeManager) provider.GetRequiredService(
-                typeof(OpenIddictScopeManager<>).MakeGenericType(options.DefaultScopeType));
+                typeof(OpenIddictScopeManager<>).MakeGenericType(type));
         });
 
-        builder.Services.TryAddScoped(provider =>
+        builder.Services.TryAddScoped(static provider =>
         {
-            var options = provider.GetRequiredService<IOptionsMonitor<OpenIddictCoreOptions>>().CurrentValue;
-            if (options.DefaultTokenType is null)
-            {
+            var type = provider.GetRequiredService<IOptionsMonitor<OpenIddictCoreOptions>>()
+                .CurrentValue?.DefaultTokenType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0276));
-            }
 
             return (IOpenIddictTokenManager) provider.GetRequiredService(
-                typeof(OpenIddictTokenManager<>).MakeGenericType(options.DefaultTokenType));
+                typeof(OpenIddictTokenManager<>).MakeGenericType(type));
         });
 
         return new OpenIddictCoreBuilder(builder.Services);

src/OpenIddict.EntityFramework/Resolvers/OpenIddictEntityFrameworkApplicationStoreResolver.cs

@@ -47,17 +47,11 @@ public class OpenIddictEntityFrameworkApplicationStoreResolver : IOpenIddictAppl
 
         var type = _cache.GetOrAdd(typeof(TApplication), key =>
         {
-            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkApplication<,,>));
-            if (root is null)
-            {
+            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkApplication<,,>)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0234));
-            }
 
-            var context = _options.CurrentValue.DbContextType;
-            if (context is null)
-            {
+            var context = _options.CurrentValue.DbContextType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0235));
-            }
 
             return typeof(OpenIddictEntityFrameworkApplicationStore<,,,,>).MakeGenericType(
                 /* TApplication: */ key,

src/OpenIddict.EntityFramework/Resolvers/OpenIddictEntityFrameworkAuthorizationStoreResolver.cs

@@ -47,17 +47,11 @@ public class OpenIddictEntityFrameworkAuthorizationStoreResolver : IOpenIddictAu
 
         var type = _cache.GetOrAdd(typeof(TAuthorization), key =>
         {
-            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkAuthorization<,,>));
-            if (root is null)
-            {
+            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkAuthorization<,,>)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0236));
-            }
 
-            var context = _options.CurrentValue.DbContextType;
-            if (context is null)
-            {
+            var context = _options.CurrentValue.DbContextType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0235));
-            }
 
             return typeof(OpenIddictEntityFrameworkAuthorizationStore<,,,,>).MakeGenericType(
                 /* TAuthorization: */ key,

src/OpenIddict.EntityFramework/Resolvers/OpenIddictEntityFrameworkScopeStoreResolver.cs

@@ -47,17 +47,11 @@ public class OpenIddictEntityFrameworkScopeStoreResolver : IOpenIddictScopeStore
 
         var type = _cache.GetOrAdd(typeof(TScope), key =>
         {
-            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkScope<>));
-            if (root is null)
-            {
+            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkScope<>)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0237));
-            }
 
-            var context = _options.CurrentValue.DbContextType;
-            if (context is null)
-            {
+            var context = _options.CurrentValue.DbContextType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0235));
-            }
 
             return typeof(OpenIddictEntityFrameworkScopeStore<,,>).MakeGenericType(
                 /* TScope: */ key,

src/OpenIddict.EntityFramework/Resolvers/OpenIddictEntityFrameworkTokenStoreResolver.cs

@@ -47,17 +47,11 @@ public class OpenIddictEntityFrameworkTokenStoreResolver : IOpenIddictTokenStore
 
         var type = _cache.GetOrAdd(typeof(TToken), key =>
         {
-            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkToken<,,>));
-            if (root is null)
-            {
+            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkToken<,,>)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0238));
-            }
 
-            var context = _options.CurrentValue.DbContextType;
-            if (context is null)
-            {
+            var context = _options.CurrentValue.DbContextType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0235));
-            }
 
             return typeof(OpenIddictEntityFrameworkTokenStore<,,,,>).MakeGenericType(
                 /* TToken: */ key,

src/OpenIddict.EntityFramework/Stores/OpenIddictEntityFrameworkApplicationStore.cs

@@ -610,7 +610,7 @@ public class OpenIddictEntityFrameworkApplicationStore<TApplication, TAuthorizat
     public virtual ValueTask SetDisplayNamesAsync(TApplication application!!,
         ImmutableDictionary<CultureInfo, string> names, CancellationToken cancellationToken)
     {
-        if (names is null || names.IsEmpty)
+        if (names is not { Count: > 0 })
         {
             application.DisplayNames = null;
 
@@ -709,7 +709,7 @@ public class OpenIddictEntityFrameworkApplicationStore<TApplication, TAuthorizat
     public virtual ValueTask SetPropertiesAsync(TApplication application!!,
         ImmutableDictionary<string, JsonElement> properties, CancellationToken cancellationToken)
     {
-        if (properties is not { IsEmpty: false })
+        if (properties is not { Count: > 0 })
         {
             application.Properties = null;
 

src/OpenIddict.EntityFramework/Stores/OpenIddictEntityFrameworkAuthorizationStore.cs

@@ -587,13 +587,9 @@ public class OpenIddictEntityFrameworkAuthorizationStore<TAuthorization, TApplic
     {
         if (!string.IsNullOrEmpty(identifier))
         {
-            var application = await Applications.FindAsync(cancellationToken, ConvertIdentifierFromString(identifier));
-            if (application is null)
-            {
+            authorization.Application = await Applications.FindAsync(
+                cancellationToken, ConvertIdentifierFromString(identifier)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0244));
-            }
-
-            authorization.Application = application;
         }
 
         else
@@ -627,7 +623,7 @@ public class OpenIddictEntityFrameworkAuthorizationStore<TAuthorization, TApplic
     public virtual ValueTask SetPropertiesAsync(TAuthorization authorization!!,
         ImmutableDictionary<string, JsonElement> properties, CancellationToken cancellationToken)
     {
-        if (properties is not { IsEmpty: false })
+        if (properties is not { Count: > 0 })
         {
             authorization.Properties = null;
 

src/OpenIddict.EntityFramework/Stores/OpenIddictEntityFrameworkScopeStore.cs

@@ -402,7 +402,7 @@ public class OpenIddictEntityFrameworkScopeStore<TScope, TContext, TKey> : IOpen
     public virtual ValueTask SetDescriptionsAsync(TScope scope!!,
         ImmutableDictionary<CultureInfo, string> descriptions, CancellationToken cancellationToken)
     {
-        if (descriptions is null || descriptions.IsEmpty)
+        if (descriptions is not { Count: > 0 })
         {
             scope.Descriptions = null;
 
@@ -444,7 +444,7 @@ public class OpenIddictEntityFrameworkScopeStore<TScope, TContext, TKey> : IOpen
     public virtual ValueTask SetDisplayNamesAsync(TScope scope!!,
         ImmutableDictionary<CultureInfo, string> names, CancellationToken cancellationToken)
     {
-        if (names is null || names.IsEmpty)
+        if (names is not { Count: > 0 })
         {
             scope.DisplayNames = null;
 
@@ -486,7 +486,7 @@ public class OpenIddictEntityFrameworkScopeStore<TScope, TContext, TKey> : IOpen
     public virtual ValueTask SetPropertiesAsync(TScope scope!!,
         ImmutableDictionary<string, JsonElement> properties, CancellationToken cancellationToken)
     {
-        if (properties is not { IsEmpty: false })
+        if (properties is not { Count: > 0 })
         {
             scope.Properties = null;
 

src/OpenIddict.EntityFramework/Stores/OpenIddictEntityFrameworkTokenStore.cs

@@ -530,13 +530,9 @@ public class OpenIddictEntityFrameworkTokenStore<TToken, TApplication, TAuthoriz
     {
         if (!string.IsNullOrEmpty(identifier))
         {
-            var application = await Applications.FindAsync(cancellationToken, ConvertIdentifierFromString(identifier));
-            if (application is null)
-            {
+            token.Application = await Applications.FindAsync(
+                cancellationToken, ConvertIdentifierFromString(identifier)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0250));
-            }
-
-            token.Application = application;
         }
 
         else
@@ -562,13 +558,9 @@ public class OpenIddictEntityFrameworkTokenStore<TToken, TApplication, TAuthoriz
     {
         if (!string.IsNullOrEmpty(identifier))
         {
-            var authorization = await Authorizations.FindAsync(cancellationToken, ConvertIdentifierFromString(identifier));
-            if (authorization is null)
-            {
+            token.Authorization = await Authorizations.FindAsync(
+                cancellationToken, ConvertIdentifierFromString(identifier)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0251));
-            }
-
-            token.Authorization = authorization;
         }
 
         else

src/OpenIddict.EntityFrameworkCore/Resolvers/OpenIddictEntityFrameworkCoreApplicationStoreResolver.cs

@@ -47,17 +47,11 @@ public class OpenIddictEntityFrameworkCoreApplicationStoreResolver : IOpenIddict
 
         var type = _cache.GetOrAdd(typeof(TApplication), key =>
         {
-            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkCoreApplication<,,>));
-            if (root is null)
-            {
+            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkCoreApplication<,,>)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0252));
-            }
 
-            var context = _options.CurrentValue.DbContextType;
-            if (context is null)
-            {
+            var context = _options.CurrentValue.DbContextType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0253));
-            }
 
             return typeof(OpenIddictEntityFrameworkCoreApplicationStore<,,,,>).MakeGenericType(
                 /* TApplication: */ key,

src/OpenIddict.EntityFrameworkCore/Resolvers/OpenIddictEntityFrameworkCoreAuthorizationStoreResolver.cs

@@ -47,17 +47,11 @@ public class OpenIddictEntityFrameworkCoreAuthorizationStoreResolver : IOpenIddi
 
         var type = _cache.GetOrAdd(typeof(TAuthorization), key =>
         {
-            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkCoreAuthorization<,,>));
-            if (root is null)
-            {
+            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkCoreAuthorization<,,>)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0254));
-            }
 
-            var context = _options.CurrentValue.DbContextType;
-            if (context is null)
-            {
+            var context = _options.CurrentValue.DbContextType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0253));
-            }
 
             return typeof(OpenIddictEntityFrameworkCoreAuthorizationStore<,,,,>).MakeGenericType(
                 /* TAuthorization: */ key,

src/OpenIddict.EntityFrameworkCore/Resolvers/OpenIddictEntityFrameworkCoreScopeStoreResolver.cs

@@ -47,17 +47,11 @@ public class OpenIddictEntityFrameworkCoreScopeStoreResolver : IOpenIddictScopeS
 
         var type = _cache.GetOrAdd(typeof(TScope), key =>
         {
-            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkCoreScope<>));
-            if (root is null)
-            {
+            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkCoreScope<>)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0255));
-            }
 
-            var context = _options.CurrentValue.DbContextType;
-            if (context is null)
-            {
+            var context = _options.CurrentValue.DbContextType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0253));
-            }
 
             return typeof(OpenIddictEntityFrameworkCoreScopeStore<,,>).MakeGenericType(
                 /* TScope: */ key,

src/OpenIddict.EntityFrameworkCore/Resolvers/OpenIddictEntityFrameworkCoreTokenStoreResolver.cs

@@ -47,17 +47,11 @@ public class OpenIddictEntityFrameworkCoreTokenStoreResolver : IOpenIddictTokenS
 
         var type = _cache.GetOrAdd(typeof(TToken), key =>
         {
-            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkCoreToken<,,>));
-            if (root is null)
-            {
+            var root = OpenIddictHelpers.FindGenericBaseType(key, typeof(OpenIddictEntityFrameworkCoreToken<,,>)) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0256));
-            }
 
-            var context = _options.CurrentValue.DbContextType;
-            if (context is null)
-            {
+            var context = _options.CurrentValue.DbContextType ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0253));
-            }
 
             return typeof(OpenIddictEntityFrameworkCoreTokenStore<,,,,>).MakeGenericType(
                 /* TToken: */ key,

src/OpenIddict.EntityFrameworkCore/Stores/OpenIddictEntityFrameworkCoreApplicationStore.cs

@@ -649,7 +649,7 @@ public class OpenIddictEntityFrameworkCoreApplicationStore<TApplication, TAuthor
     public virtual ValueTask SetDisplayNamesAsync(TApplication application!!,
         ImmutableDictionary<CultureInfo, string> names, CancellationToken cancellationToken)
     {
-        if (names is null || names.IsEmpty)
+        if (names is not { Count: > 0 })
         {
             application.DisplayNames = null;
 
@@ -748,7 +748,7 @@ public class OpenIddictEntityFrameworkCoreApplicationStore<TApplication, TAuthor
     public virtual ValueTask SetPropertiesAsync(TApplication application!!,
         ImmutableDictionary<string, JsonElement> properties, CancellationToken cancellationToken)
     {
-        if (properties is not { IsEmpty: false })
+        if (properties is not { Count: > 0 })
         {
             application.Properties = null;
 

src/OpenIddict.EntityFrameworkCore/Stores/OpenIddictEntityFrameworkCoreAuthorizationStore.cs

@@ -671,17 +671,10 @@ public class OpenIddictEntityFrameworkCoreAuthorizationStore<TAuthorization, TAp
 
             // Warning: FindAsync() is deliberately not used to work around a breaking change introduced
             // in Entity Framework Core 3.x (where a ValueTask instead of a Task is now returned).
-            var application =
-                await Applications.AsQueryable()
-                                  .AsTracking()
-                                  .FirstOrDefaultAsync(application => application.Id!.Equals(key), cancellationToken);
-
-            if (application is null)
-            {
+            authorization.Application = await Applications.AsQueryable()
+                .AsTracking()
+                .FirstOrDefaultAsync(application => application.Id!.Equals(key), cancellationToken) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0244));
-            }
-
-            authorization.Application = application;
         }
 
         else
@@ -715,7 +708,7 @@ public class OpenIddictEntityFrameworkCoreAuthorizationStore<TAuthorization, TAp
     public virtual ValueTask SetPropertiesAsync(TAuthorization authorization!!,
         ImmutableDictionary<string, JsonElement> properties, CancellationToken cancellationToken)
     {
-        if (properties is not { IsEmpty: false })
+        if (properties is not { Count: > 0 })
         {
             authorization.Properties = null;
 

src/OpenIddict.EntityFrameworkCore/Stores/OpenIddictEntityFrameworkCoreScopeStore.cs

@@ -416,7 +416,7 @@ public class OpenIddictEntityFrameworkCoreScopeStore<TScope, TContext, TKey> : I
     public virtual ValueTask SetDescriptionsAsync(TScope scope!!,
         ImmutableDictionary<CultureInfo, string> descriptions, CancellationToken cancellationToken)
     {
-        if (descriptions is null || descriptions.IsEmpty)
+        if (descriptions is not { Count: > 0 })
         {
             scope.Descriptions = null;
 
@@ -458,7 +458,7 @@ public class OpenIddictEntityFrameworkCoreScopeStore<TScope, TContext, TKey> : I
     public virtual ValueTask SetDisplayNamesAsync(TScope scope!!,
         ImmutableDictionary<CultureInfo, string> names, CancellationToken cancellationToken)
     {
-        if (names is null || names.IsEmpty)
+        if (names is not { Count: > 0 })
         {
             scope.DisplayNames = null;
 
@@ -500,7 +500,7 @@ public class OpenIddictEntityFrameworkCoreScopeStore<TScope, TContext, TKey> : I
     public virtual ValueTask SetPropertiesAsync(TScope scope!!,
         ImmutableDictionary<string, JsonElement> properties, CancellationToken cancellationToken)
     {
-        if (properties is not { IsEmpty: false })
+        if (properties is not { Count: > 0 })
         {
             scope.Properties = null;
 

src/OpenIddict.EntityFrameworkCore/Stores/OpenIddictEntityFrameworkCoreTokenStore.cs

@@ -594,17 +594,10 @@ public class OpenIddictEntityFrameworkCoreTokenStore<TToken, TApplication, TAuth
 
             // Warning: FindAsync() is deliberately not used to work around a breaking change introduced
             // in Entity Framework Core 3.x (where a ValueTask instead of a Task is now returned).
-            var application =
-                await Applications.AsQueryable()
-                                  .AsTracking()
-                                  .FirstOrDefaultAsync(application => application.Id!.Equals(key), cancellationToken);
-
-            if (application is null)
-            {
+            token.Application = await Applications.AsQueryable()
+                .AsTracking()
+                .FirstOrDefaultAsync(application => application.Id!.Equals(key), cancellationToken) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0250));
-            }
-
-            token.Application = application;
         }
 
         else
@@ -634,17 +627,10 @@ public class OpenIddictEntityFrameworkCoreTokenStore<TToken, TApplication, TAuth
 
             // Warning: FindAsync() is deliberately not used to work around a breaking change introduced
             // in Entity Framework Core 3.x (where a ValueTask instead of a Task is now returned).
-            var authorization =
-                await Authorizations.AsQueryable()
-                                    .AsTracking()
-                                    .FirstOrDefaultAsync(authorization => authorization.Id!.Equals(key), cancellationToken);
-
-            if (authorization is null)
-            {
+            token.Authorization = await Authorizations.AsQueryable()
+                .AsTracking()
+                .FirstOrDefaultAsync(authorization => authorization.Id!.Equals(key), cancellationToken) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0251));
-            }
-
-            token.Authorization = authorization;
         }
 
         else

src/OpenIddict.MongoDb/Stores/OpenIddictMongoDbApplicationStore.cs

@@ -387,7 +387,7 @@ public class OpenIddictMongoDbApplicationStore<TApplication> : IOpenIddictApplic
     public virtual ValueTask SetPropertiesAsync(TApplication application!!,
         ImmutableDictionary<string, JsonElement> properties, CancellationToken cancellationToken)
     {
-        if (properties is not { IsEmpty: false })
+        if (properties is not { Count: > 0 })
         {
             application.Properties = null;
 

src/OpenIddict.MongoDb/Stores/OpenIddictMongoDbAuthorizationStore.cs

@@ -509,7 +509,7 @@ public class OpenIddictMongoDbAuthorizationStore<TAuthorization> : IOpenIddictAu
     public virtual ValueTask SetPropertiesAsync(TAuthorization authorization!!,
         ImmutableDictionary<string, JsonElement> properties, CancellationToken cancellationToken)
     {
-        if (properties is not { IsEmpty: false })
+        if (properties is not { Count: > 0 })
         {
             authorization.Properties = null;
 

src/OpenIddict.MongoDb/Stores/OpenIddictMongoDbScopeStore.cs

@@ -319,7 +319,7 @@ public class OpenIddictMongoDbScopeStore<TScope> : IOpenIddictScopeStore<TScope>
     public virtual ValueTask SetPropertiesAsync(TScope scope!!,
         ImmutableDictionary<string, JsonElement> properties, CancellationToken cancellationToken)
     {
-        if (properties is not { IsEmpty: false })
+        if (properties is not { Count: > 0 })
         {
             scope.Properties = null;
 

src/OpenIddict.Server.AspNetCore/OpenIddictServerAspNetCoreHandlers.cs

@@ -1134,7 +1134,7 @@ public static partial class OpenIddictServerAspNetCoreHandlers
             // If it was not registered or enabled, let the default OpenIddict server handlers render
             // a default error page instead of delegating the rendering to the status code middleware.
             var feature = response.HttpContext.Features.Get<IStatusCodePagesFeature>();
-            if (feature is null || !feature.Enabled)
+            if (feature is not { Enabled: true })
             {
                 return default;
             }

src/OpenIddict.Server.Owin/OpenIddictServerOwinHandler.cs

@@ -109,11 +109,8 @@ public class OpenIddictServerOwinHandler : AuthenticationHandler<OpenIddictServe
     /// <inheritdoc/>
     protected override async Task<AuthenticationTicket?> AuthenticateCoreAsync()
     {
-        var transaction = Context.Get<OpenIddictServerTransaction>(typeof(OpenIddictServerTransaction).FullName);
-        if (transaction is null)
-        {
+        var transaction = Context.Get<OpenIddictServerTransaction>(typeof(OpenIddictServerTransaction).FullName) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0112));
-        }
 
         // Note: in many cases, the authentication token was already validated by the time this action is called
         // (generally later in the pipeline, when using the pass-through mode). To avoid having to re-validate it,

src/OpenIddict.Server.Owin/OpenIddictServerOwinMiddlewareFactory.cs

@@ -35,11 +35,8 @@ public class OpenIddictServerOwinMiddlewareFactory : OwinMiddleware
     /// </returns>
     public override Task Invoke(IOwinContext context!!)
     {
-        var provider = context.Get<IServiceProvider>(typeof(IServiceProvider).FullName);
-        if (provider is null)
-        {
+        var provider = context.Get<IServiceProvider>(typeof(IServiceProvider).FullName) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0121));
-        }
 
         // Note: the Microsoft.Extensions.DependencyInjection container doesn't support resolving services
         // with arbitrary parameters, which prevents the server OWIN middleware from being resolved directly

src/OpenIddict.Server/OpenIddictServerBuilder.cs

@@ -381,11 +381,8 @@ public class OpenIddictServerBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0062), nameof(resource));
         }
 
-        using var stream = assembly.GetManifestResourceStream(resource);
-        if (stream is null)
-        {
+        using var stream = assembly.GetManifestResourceStream(resource) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0064));
-        }
 
         return AddEncryptionCertificate(stream, password, flags);
     }
@@ -438,13 +435,10 @@ public class OpenIddictServerBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0065), nameof(thumbprint));
         }
 
-        var certificate = GetCertificate(StoreLocation.CurrentUser, thumbprint) ?? GetCertificate(StoreLocation.LocalMachine, thumbprint);
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddEncryptionCertificate(certificate);
+        return AddEncryptionCertificate(
+            GetCertificate(StoreLocation.CurrentUser, thumbprint)  ??
+            GetCertificate(StoreLocation.LocalMachine, thumbprint) ??
+            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
 
         static X509Certificate2? GetCertificate(StoreLocation location, string thumbprint)
         {
@@ -474,16 +468,10 @@ public class OpenIddictServerBuilder
         using var store = new X509Store(name, location);
         store.Open(OpenFlags.ReadOnly);
 
-        var certificate = store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
-            .OfType<X509Certificate2>()
-            .SingleOrDefault();
-
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddEncryptionCertificate(certificate);
+        return AddEncryptionCertificate(
+            store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
+                .OfType<X509Certificate2>()
+                .SingleOrDefault() ?? throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
     }
 
     /// <summary>
@@ -789,11 +777,8 @@ public class OpenIddictServerBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0062), nameof(resource));
         }
 
-        using var stream = assembly.GetManifestResourceStream(resource);
-        if (stream is null)
-        {
+        using var stream = assembly.GetManifestResourceStream(resource) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0064));
-        }
 
         return AddSigningCertificate(stream, password, flags);
     }
@@ -846,13 +831,10 @@ public class OpenIddictServerBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0065), nameof(thumbprint));
         }
 
-        var certificate = GetCertificate(StoreLocation.CurrentUser, thumbprint) ?? GetCertificate(StoreLocation.LocalMachine, thumbprint);
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddSigningCertificate(certificate);
+        return AddSigningCertificate(
+            GetCertificate(StoreLocation.CurrentUser, thumbprint)  ??
+            GetCertificate(StoreLocation.LocalMachine, thumbprint) ??
+            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
 
         static X509Certificate2? GetCertificate(StoreLocation location, string thumbprint)
         {
@@ -882,16 +864,11 @@ public class OpenIddictServerBuilder
         using var store = new X509Store(name, location);
         store.Open(OpenFlags.ReadOnly);
 
-        var certificate = store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
-            .OfType<X509Certificate2>()
-            .SingleOrDefault();
 
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddSigningCertificate(certificate);
+        return AddSigningCertificate(
+            store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
+                .OfType<X509Certificate2>()
+                .SingleOrDefault() ?? throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
     }
 
     /// <summary>

src/OpenIddict.Server/OpenIddictServerDispatcher.cs

@@ -93,16 +93,15 @@ public class OpenIddictServerDispatcher : IOpenIddictServerDispatcher
                     continue;
                 }
 
-                var handler = descriptor.ServiceDescriptor.ImplementationInstance is not null ?
-                    descriptor.ServiceDescriptor.ImplementationInstance as IOpenIddictServerHandler<TContext> :
-                    _provider.GetService(descriptor.ServiceDescriptor.ServiceType) as IOpenIddictServerHandler<TContext>;
-
-                if (handler is null)
+                yield return descriptor.ServiceDescriptor switch
                 {
-                    throw new InvalidOperationException(SR.FormatID0098(descriptor.ServiceDescriptor.ServiceType));
-                }
+                    { ImplementationInstance: IOpenIddictServerHandler<TContext> handler } => handler,
+
+                    _ when _provider.GetService(descriptor.ServiceDescriptor.ServiceType)
+                        is IOpenIddictServerHandler<TContext> handler => handler,
 
-                yield return handler;
+                    _ => throw new InvalidOperationException(SR.FormatID0098(descriptor.ServiceDescriptor.ServiceType))
+                };
             }
         }
 

src/OpenIddict.Server/OpenIddictServerHandlers.Authentication.cs

@@ -1001,11 +1001,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // To prevent downgrade attacks, ensure that authorization requests returning an access token directly
                 // from the authorization endpoint are rejected if the client_id corresponds to a confidential application
@@ -1061,11 +1058,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // If no explicit redirect_uri was specified, retrieve the addresses associated with
                 // the client and ensure exactly one redirect_uri was attached to the client definition.
@@ -1208,11 +1202,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Reject the request if the application is not allowed to use the authorization endpoint.
                 if (!await _applicationManager.HasPermissionAsync(application, Permissions.Endpoints.Authorization))
@@ -1259,11 +1250,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Reject the request if the application is not allowed to use the authorization code grant.
                 if (context.Request.IsAuthorizationCodeFlow() &&
@@ -1355,11 +1343,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Reject requests that specify a response_type for which no permission was granted.
                 if (!await HasPermissionAsync(context.Request.GetResponseTypes()))
@@ -1433,11 +1418,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 foreach (var scope in context.Request.GetScopes())
                 {
@@ -1501,11 +1483,8 @@ public static partial class OpenIddictServerHandlers
                     return;
                 }
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 if (await _applicationManager.HasRequirementAsync(application, Requirements.Features.ProofKeyForCodeExchange))
                 {

src/OpenIddict.Server/OpenIddictServerHandlers.Device.cs

@@ -527,11 +527,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 if (await _applicationManager.HasClientTypeAsync(application, ClientTypes.Public))
                 {
@@ -596,11 +593,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // If the application is a public client, don't validate the client secret.
                 if (await _applicationManager.HasClientTypeAsync(application, ClientTypes.Public))
@@ -656,11 +650,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Reject the request if the application is not allowed to use the device endpoint.
                 if (!await _applicationManager.HasPermissionAsync(application, Permissions.Endpoints.Device))
@@ -707,11 +698,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Reject the request if the application is not allowed to use the device code grant.
                 if (!await _applicationManager.HasPermissionAsync(application, Permissions.GrantTypes.DeviceCode))
@@ -775,11 +763,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 foreach (var scope in context.Request.GetScopes())
                 {

src/OpenIddict.Server/OpenIddictServerHandlers.Discovery.cs

@@ -1170,7 +1170,7 @@ public static partial class OpenIddictServerHandlers
                     return certificate.GetCertHash(algorithm);
 #else
                     using var hash = CryptoConfig.CreateFromName(algorithm.Name!) as HashAlgorithm;
-                    if (hash is null || hash is KeyedHashAlgorithm)
+                    if (hash is null or KeyedHashAlgorithm)
                     {
                         throw new InvalidOperationException(SR.GetResourceString(SR.ID0217));
                     }

src/OpenIddict.Server/OpenIddictServerHandlers.Exchange.cs

@@ -801,11 +801,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 if (await _applicationManager.HasClientTypeAsync(application, ClientTypes.Public))
                 {
@@ -883,11 +880,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // If the application is a public client, don't validate the client secret.
                 if (await _applicationManager.HasClientTypeAsync(application, ClientTypes.Public))
@@ -943,11 +937,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Reject the request if the application is not allowed to use the token endpoint.
                 if (!await _applicationManager.HasPermissionAsync(application, Permissions.Endpoints.Token))
@@ -996,11 +987,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Reject the request if the application is not allowed to use the specified grant type.
                 if (!await _applicationManager.HasPermissionAsync(application, Permissions.Prefixes.GrantType + context.Request.GrantType))
@@ -1064,11 +1052,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 foreach (var scope in context.Request.GetScopes())
                 {
@@ -1138,11 +1123,8 @@ public static partial class OpenIddictServerHandlers
 
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 if (await _applicationManager.HasRequirementAsync(application, Requirements.Features.ProofKeyForCodeExchange))
                 {

src/OpenIddict.Server/OpenIddictServerHandlers.Introspection.cs

@@ -458,11 +458,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 if (await _applicationManager.HasClientTypeAsync(application, ClientTypes.Public))
                 {
@@ -527,11 +524,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // If the application is a public client, don't validate the client secret.
                 if (await _applicationManager.HasClientTypeAsync(application, ClientTypes.Public))
@@ -587,11 +581,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Reject the request if the application is not allowed to use the introspection endpoint.
                 if (!await _applicationManager.HasPermissionAsync(application, Permissions.Endpoints.Introspection))
@@ -887,11 +878,8 @@ public static partial class OpenIddictServerHandlers
                     return;
                 }
 
-                var application = await _applicationManager.FindByClientIdAsync(context.Request.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.Request.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Public clients are not allowed to access sensitive claims as authentication cannot be enforced.
                 if (await _applicationManager.HasClientTypeAsync(application, ClientTypes.Public))

src/OpenIddict.Server/OpenIddictServerHandlers.Protection.cs

@@ -545,11 +545,8 @@ public static partial class OpenIddictServerHandlers
                     return;
                 }
 
-                var token = await _tokenManager.FindByIdAsync(context.TokenId);
-                if (token is null)
-                {
+                var token = await _tokenManager.FindByIdAsync(context.TokenId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0021));
-                }
 
                 // Restore the creation/expiration dates/identifiers from the token entry metadata.
                 context.Principal.SetCreationDate(await _tokenManager.GetCreationDateAsync(token))
@@ -1060,20 +1057,14 @@ public static partial class OpenIddictServerHandlers
                 // If the client application is known, associate it with the token.
                 if (!string.IsNullOrEmpty(context.ClientId))
                 {
-                    var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                    if (application is null)
-                    {
+                    var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                         throw new InvalidOperationException(SR.GetResourceString(SR.ID0017));
-                    }
 
                     descriptor.ApplicationId = await _applicationManager.GetIdAsync(application);
                 }
 
-                var token = await _tokenManager.CreateAsync(descriptor);
-                if (token is null)
-                {
+                var token = await _tokenManager.CreateAsync(descriptor) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0019));
-                }
 
                 var identifier = await _tokenManager.GetIdAsync(token);
 
@@ -1237,11 +1228,8 @@ public static partial class OpenIddictServerHandlers
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0009));
                 }
 
-                var token = await _tokenManager.FindByIdAsync(identifier);
-                if (token is null)
-                {
+                var token = await _tokenManager.FindByIdAsync(identifier) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0021));
-                }
 
                 var descriptor = new OpenIddictTokenDescriptor();
                 await _tokenManager.PopulateAsync(descriptor, token);

src/OpenIddict.Server/OpenIddictServerHandlers.Revocation.cs

@@ -405,11 +405,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 if (await _applicationManager.HasClientTypeAsync(application, ClientTypes.Public))
                 {
@@ -474,11 +471,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // If the application is a public client, don't validate the client secret.
                 if (await _applicationManager.HasClientTypeAsync(application, ClientTypes.Public))
@@ -534,11 +528,8 @@ public static partial class OpenIddictServerHandlers
             {
                 Debug.Assert(!string.IsNullOrEmpty(context.ClientId), SR.FormatID4000(Parameters.ClientId));
 
-                var application = await _applicationManager.FindByClientIdAsync(context.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0032));
-                }
 
                 // Reject the request if the application is not allowed to use the revocation endpoint.
                 if (!await _applicationManager.HasPermissionAsync(application, Permissions.Endpoints.Revocation))

src/OpenIddict.Server/OpenIddictServerHandlers.cs

@@ -1427,20 +1427,14 @@ public static partial class OpenIddictServerHandlers
             // If the client application is known, associate it to the authorization.
             if (!string.IsNullOrEmpty(context.Request.ClientId))
             {
-                var application = await _applicationManager.FindByClientIdAsync(context.Request.ClientId);
-                if (application is null)
-                {
+                var application = await _applicationManager.FindByClientIdAsync(context.Request.ClientId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0017));
-                }
 
                 descriptor.ApplicationId = await _applicationManager.GetIdAsync(application);
             }
 
-            var authorization = await _authorizationManager.CreateAsync(descriptor);
-            if (authorization is null)
-            {
+            var authorization = await _authorizationManager.CreateAsync(descriptor) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0018));
-            }
 
             var identifier = await _authorizationManager.GetIdAsync(authorization);
 
@@ -2368,11 +2362,8 @@ public static partial class OpenIddictServerHandlers
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0008));
             }
 
-            var token = await _tokenManager.FindByIdAsync(identifier);
-            if (token is null)
-            {
+            var token = await _tokenManager.FindByIdAsync(identifier) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0265));
-            }
 
             // Replace the device code details by the payload derived from the new device code principal,
             // that includes all the user claims populated by the application after authenticating the user.
@@ -2423,14 +2414,11 @@ public static partial class OpenIddictServerHandlers
             }
 
             var credentials = context.Options.SigningCredentials.Find(
-                credentials => credentials.Key is AsymmetricSecurityKey);
-            if (credentials is null)
-            {
+                credentials => credentials.Key is AsymmetricSecurityKey) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0266));
-            }
 
             using var algorithm = GetHashAlgorithm(credentials);
-            if (algorithm is null || algorithm is KeyedHashAlgorithm)
+            if (algorithm is null or KeyedHashAlgorithm)
             {
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0267));
             }

src/OpenIddict.Validation.Owin/OpenIddictValidationOwinMiddlewareFactory.cs

@@ -35,11 +35,8 @@ public class OpenIddictValidationOwinMiddlewareFactory : OwinMiddleware
     /// </returns>
     public override Task Invoke(IOwinContext context!!)
     {
-        var provider = context.Get<IServiceProvider>(typeof(IServiceProvider).FullName);
-        if (provider is null)
-        {
+        var provider = context.Get<IServiceProvider>(typeof(IServiceProvider).FullName) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0168));
-        }
 
         // Note: the Microsoft.Extensions.DependencyInjection container doesn't support resolving services
         // with arbitrary parameters, which prevents the validation OWIN middleware from being resolved directly

src/OpenIddict.Validation.SystemNetHttp/OpenIddictValidationSystemNetHttpHandlers.cs

@@ -221,21 +221,15 @@ public static partial class OpenIddictValidationSystemNetHttpHandlers
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0173));
 
             var assembly = typeof(OpenIddictValidationSystemNetHttpOptions).Assembly.GetName();
-            using var client = _factory.CreateClient(assembly.Name!);
-            if (client is null)
-            {
+            using var client = _factory.CreateClient(assembly.Name!) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0174));
-            }
 
 #if SUPPORTS_HTTP_CLIENT_DEFAULT_REQUEST_VERSION
             // If supported, import the HTTP version from the client instance.
             request.Version = client.DefaultRequestVersion;
 #endif
-            var response = await client.SendAsync(request, HttpCompletionOption.ResponseContentRead);
-            if (response is null)
-            {
+            var response = await client.SendAsync(request, HttpCompletionOption.ResponseContentRead) ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0175));
-            }
 
             // Store the HttpResponseMessage in the transaction properties.
             context.Transaction.SetProperty(typeof(HttpResponseMessage).FullName!, response);

src/OpenIddict.Validation/OpenIddictValidationBuilder.cs

@@ -202,11 +202,8 @@ public class OpenIddictValidationBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0062), nameof(resource));
         }
 
-        using var stream = assembly.GetManifestResourceStream(resource);
-        if (stream is null)
-        {
+        using var stream = assembly.GetManifestResourceStream(resource) ??
             throw new InvalidOperationException(SR.GetResourceString(SR.ID0064));
-        }
 
         return AddEncryptionCertificate(stream, password, flags);
     }
@@ -260,13 +257,10 @@ public class OpenIddictValidationBuilder
             throw new ArgumentException(SR.GetResourceString(SR.ID0065), nameof(thumbprint));
         }
 
-        var certificate = GetCertificate(StoreLocation.CurrentUser, thumbprint) ?? GetCertificate(StoreLocation.LocalMachine, thumbprint);
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddEncryptionCertificate(certificate);
+        return AddEncryptionCertificate(
+            GetCertificate(StoreLocation.CurrentUser, thumbprint)  ??
+            GetCertificate(StoreLocation.LocalMachine, thumbprint) ??
+            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
 
         static X509Certificate2? GetCertificate(StoreLocation location, string thumbprint)
         {
@@ -297,16 +291,11 @@ public class OpenIddictValidationBuilder
         using var store = new X509Store(name, location);
         store.Open(OpenFlags.ReadOnly);
 
-        var certificate = store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
-            .OfType<X509Certificate2>()
-            .SingleOrDefault();
 
-        if (certificate is null)
-        {
-            throw new InvalidOperationException(SR.GetResourceString(SR.ID0066));
-        }
-
-        return AddEncryptionCertificate(certificate);
+        return AddEncryptionCertificate(
+            store.Certificates.Find(X509FindType.FindByThumbprint, thumbprint, validOnly: false)
+                .OfType<X509Certificate2>()
+                .SingleOrDefault() ?? throw new InvalidOperationException(SR.GetResourceString(SR.ID0066)));
     }
 
     /// <summary>

src/OpenIddict.Validation/OpenIddictValidationDispatcher.cs

@@ -93,16 +93,15 @@ public class OpenIddictValidationDispatcher : IOpenIddictValidationDispatcher
                     continue;
                 }
 
-                var handler = descriptor.ServiceDescriptor.ImplementationInstance is not null ?
-                    descriptor.ServiceDescriptor.ImplementationInstance as IOpenIddictValidationHandler<TContext> :
-                    _provider.GetService(descriptor.ServiceDescriptor.ServiceType) as IOpenIddictValidationHandler<TContext>;
-
-                if (handler is null)
+                yield return descriptor.ServiceDescriptor switch
                 {
-                    throw new InvalidOperationException(SR.FormatID0138(descriptor.ServiceDescriptor.ServiceType));
-                }
+                    { ImplementationInstance: IOpenIddictValidationHandler<TContext> handler } => handler,
+
+                    _ when _provider.GetService(descriptor.ServiceDescriptor.ServiceType)
+                        is IOpenIddictValidationHandler<TContext> handler => handler,
 
-                yield return handler;
+                    _ => throw new InvalidOperationException(SR.FormatID0138(descriptor.ServiceDescriptor.ServiceType))
+                };
             }
         }
 

src/OpenIddict.Validation/OpenIddictValidationHandlers.Protection.cs

@@ -545,11 +545,8 @@ public static partial class OpenIddictValidationHandlers
                     return;
                 }
 
-                var token = await _tokenManager.FindByIdAsync(context.TokenId);
-                if (token is null)
-                {
+                var token = await _tokenManager.FindByIdAsync(context.TokenId) ??
                     throw new InvalidOperationException(SR.GetResourceString(SR.ID0021));
-                }
 
                 // Restore the creation/expiration dates/identifiers from the token entry metadata.
                 context.Principal.SetCreationDate(await _tokenManager.GetCreationDateAsync(token))

src/OpenIddict.Validation/OpenIddictValidationService.cs

@@ -55,13 +55,8 @@ public class OpenIddictValidationService
             request = await ApplyConfigurationRequestAsync();
             var response = await ExtractConfigurationResponseAsync();
 
-            var configuration = await HandleConfigurationResponseAsync();
-            if (configuration is null)
-            {
+            return await HandleConfigurationResponseAsync() ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0145));
-            }
-
-            return configuration;
 
             async ValueTask<OpenIddictRequest> PrepareConfigurationRequestAsync()
             {
@@ -195,13 +190,8 @@ public class OpenIddictValidationService
 
             var response = await ExtractCryptographyResponseAsync();
 
-            var keys = await HandleCryptographyResponseAsync();
-            if (keys is null)
-            {
+            return await HandleCryptographyResponseAsync() ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0147));
-            }
-
-            return keys;
 
             async ValueTask<OpenIddictRequest> PrepareCryptographyRequestAsync()
             {
@@ -351,13 +341,8 @@ public class OpenIddictValidationService
             request = await ApplyIntrospectionRequestAsync();
             var response = await ExtractIntrospectionResponseAsync();
 
-            var principal = await HandleIntrospectionResponseAsync();
-            if (principal is null)
-            {
+            return await HandleIntrospectionResponseAsync() ??
                 throw new InvalidOperationException(SR.GetResourceString(SR.ID0157));
-            }
-
-            return principal;
 
             async ValueTask<OpenIddictRequest> PrepareIntrospectionRequestAsync()
             {

test/OpenIddict.Server.IntegrationTests/OpenIddictServerIntegrationTestClient.cs

@@ -211,7 +211,7 @@ public class OpenIddictServerIntegrationTestClient : IAsyncDisposable
             }
 
             var values = (string?[]?) parameter.Value;
-            if (values is null || values.Length == 0)
+            if (values is not { Length: > 0 })
             {
                 continue;
             }