diff --git a/framework/src/Volo.Abp.Settings/Volo.Abp.Settings.csproj b/framework/src/Volo.Abp.Settings/Volo.Abp.Settings.csproj
index 524f932e9c..efec1d42c5 100644
--- a/framework/src/Volo.Abp.Settings/Volo.Abp.Settings.csproj
+++ b/framework/src/Volo.Abp.Settings/Volo.Abp.Settings.csproj
@@ -5,6 +5,8 @@
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;netstandard2.1;net7.0</TargetFrameworks>
+    <Nullable>enable</Nullable>
+    <WarningsAsErrors>Nullable</WarningsAsErrors>
     <AssemblyName>Volo.Abp.Settings</AssemblyName>
     <PackageId>Volo.Abp.Settings</PackageId>
     <AssetTargetFallback>$(AssetTargetFallback);portable-net45+win8+wp8+wpa81;</AssetTargetFallback>
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ConfigurationSettingValueProvider.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ConfigurationSettingValueProvider.cs
index 853b510d04..51e0a882b0 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ConfigurationSettingValueProvider.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ConfigurationSettingValueProvider.cs
@@ -21,7 +21,7 @@ public class ConfigurationSettingValueProvider : ISettingValueProvider, ITransie
         Configuration = configuration;
     }
 
-    public virtual Task<string> GetOrNullAsync(SettingDefinition setting)
+    public virtual Task<string?> GetOrNullAsync(SettingDefinition setting)
     {
         return Task.FromResult(Configuration[ConfigurationNamePrefix + setting.Name]);
     }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/DefaultValueSettingValueProvider.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/DefaultValueSettingValueProvider.cs
index e5e7275281..299f9e63bc 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/DefaultValueSettingValueProvider.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/DefaultValueSettingValueProvider.cs
@@ -16,7 +16,7 @@ public class DefaultValueSettingValueProvider : SettingValueProvider
 
     }
 
-    public override Task<string> GetOrNullAsync(SettingDefinition setting)
+    public override Task<string?> GetOrNullAsync(SettingDefinition setting)
     {
         return Task.FromResult(setting.DefaultValue);
     }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/GlobalSettingValueProvider.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/GlobalSettingValueProvider.cs
index 34439c6aef..6c0e8883d7 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/GlobalSettingValueProvider.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/GlobalSettingValueProvider.cs
@@ -15,7 +15,7 @@ public class GlobalSettingValueProvider : SettingValueProvider
     {
     }
 
-    public override Task<string> GetOrNullAsync(SettingDefinition setting)
+    public override Task<string?> GetOrNullAsync(SettingDefinition setting)
     {
         return SettingStore.GetOrNullAsync(setting.Name, Name, null);
     }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingDefinitionContext.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingDefinitionContext.cs
index 8257c73adb..deecea1107 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingDefinitionContext.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingDefinitionContext.cs
@@ -4,7 +4,7 @@ namespace Volo.Abp.Settings;
 
 public interface ISettingDefinitionContext
 {
-    SettingDefinition GetOrNull(string name);
+    SettingDefinition? GetOrNull(string name);
 
     IReadOnlyList<SettingDefinition> GetAll();
 
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingDefinitionManager.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingDefinitionManager.cs
index 865fe5557a..7939d113c4 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingDefinitionManager.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingDefinitionManager.cs
@@ -10,5 +10,5 @@ public interface ISettingDefinitionManager
 
     IReadOnlyList<SettingDefinition> GetAll();
 
-    SettingDefinition GetOrNull(string name);
+    SettingDefinition? GetOrNull(string name);
 }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingEncryptionService.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingEncryptionService.cs
index f91e8f808a..5c1328e8c3 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingEncryptionService.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingEncryptionService.cs
@@ -4,9 +4,7 @@ namespace Volo.Abp.Settings;
 
 public interface ISettingEncryptionService
 {
-    [CanBeNull]
-    string Encrypt([NotNull] SettingDefinition settingDefinition, [CanBeNull] string plainValue);
+    string? Encrypt([NotNull] SettingDefinition settingDefinition, string? plainValue);
 
-    [CanBeNull]
-    string Decrypt([NotNull] SettingDefinition settingDefinition, [CanBeNull] string encryptedValue);
+    string? Decrypt([NotNull] SettingDefinition settingDefinition, string? encryptedValue);
 }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingProvider.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingProvider.cs
index d58a21b874..a24060b5ff 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingProvider.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingProvider.cs
@@ -6,7 +6,7 @@ namespace Volo.Abp.Settings;
 
 public interface ISettingProvider
 {
-    Task<string> GetOrNullAsync([NotNull] string name);
+    Task<string?> GetOrNullAsync([NotNull] string name);
 
     Task<List<SettingValue>> GetAllAsync([NotNull] string[] names);
 
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingStore.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingStore.cs
index a8be20c7d8..89f933f877 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingStore.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingStore.cs
@@ -6,15 +6,15 @@ namespace Volo.Abp.Settings;
 
 public interface ISettingStore
 {
-    Task<string> GetOrNullAsync(
+    Task<string?> GetOrNullAsync(
         [NotNull] string name,
-        [CanBeNull] string providerName,
-        [CanBeNull] string providerKey
+        string? providerName,
+        string? providerKey
     );
 
     Task<List<SettingValue>> GetAllAsync(
         [NotNull] string[] names,
-        [CanBeNull] string providerName,
-        [CanBeNull] string providerKey
+        string? providerName,
+        string? providerKey
     );
 }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingValueProvider.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingValueProvider.cs
index 6878fda17b..1619052cbd 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingValueProvider.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingValueProvider.cs
@@ -8,7 +8,7 @@ public interface ISettingValueProvider
 {
     string Name { get; }
 
-    Task<string> GetOrNullAsync([NotNull] SettingDefinition setting);
+    Task<string?> GetOrNullAsync([NotNull] SettingDefinition setting);
 
     Task<List<SettingValue>> GetAllAsync([NotNull] SettingDefinition[] settings);
 }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/NullSettingStore.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/NullSettingStore.cs
index 8db9286a14..f6d04e0b4a 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/NullSettingStore.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/NullSettingStore.cs
@@ -17,12 +17,12 @@ public class NullSettingStore : ISettingStore, ISingletonDependency
         Logger = NullLogger<NullSettingStore>.Instance;
     }
 
-    public Task<string> GetOrNullAsync(string name, string providerName, string providerKey)
+    public Task<string?> GetOrNullAsync(string name, string? providerName, string? providerKey)
     {
-        return Task.FromResult((string)null);
+        return Task.FromResult((string?)null);
     }
 
-    public Task<List<SettingValue>> GetAllAsync(string[] names, string providerName, string providerKey)
+    public Task<List<SettingValue>> GetAllAsync(string[] names, string? providerName, string? providerKey)
     {
         return Task.FromResult(names.Select(x => new SettingValue(x, null)).ToList());
     }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinition.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinition.cs
index 536a407271..72ccfcd3f3 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinition.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinition.cs
@@ -17,16 +17,14 @@ public class SettingDefinition
         get => _displayName;
         set => _displayName = Check.NotNull(value, nameof(value));
     }
-    private ILocalizableString _displayName;
+    private ILocalizableString _displayName = default!;
 
-    [CanBeNull]
-    public ILocalizableString Description { get; set; }
+    public ILocalizableString? Description { get; set; }
 
     /// <summary>
     /// Default value of the setting.
     /// </summary>
-    [CanBeNull]
-    public string DefaultValue { get; set; }
+    public string? DefaultValue { get; set; }
 
     /// <summary>
     /// Can clients see this setting and it's value.
@@ -61,9 +59,9 @@ public class SettingDefinition
 
     public SettingDefinition(
         string name,
-        string defaultValue = null,
-        ILocalizableString displayName = null,
-        ILocalizableString description = null,
+        string? defaultValue = null,
+        ILocalizableString? displayName = null,
+        ILocalizableString? description = null,
         bool isVisibleToClients = false,
         bool isInherited = true,
         bool isEncrypted = false)
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinitionContext.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinitionContext.cs
index e06395f614..a1192c96c9 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinitionContext.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinitionContext.cs
@@ -12,7 +12,7 @@ public class SettingDefinitionContext : ISettingDefinitionContext
         Settings = settings;
     }
 
-    public virtual SettingDefinition GetOrNull(string name)
+    public virtual SettingDefinition? GetOrNull(string name)
     {
         return Settings.GetOrDefault(name);
     }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinitionManager.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinitionManager.cs
index ed285422b3..87f173d04e 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinitionManager.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinitionManager.cs
@@ -45,7 +45,7 @@ public class SettingDefinitionManager : ISettingDefinitionManager, ISingletonDep
         return SettingDefinitions.Value.Values.ToImmutableList();
     }
 
-    public virtual SettingDefinition GetOrNull(string name)
+    public virtual SettingDefinition? GetOrNull(string name)
     {
         return SettingDefinitions.Value.GetOrDefault(name);
     }
@@ -63,7 +63,7 @@ public class SettingDefinitionManager : ISettingDefinitionManager, ISingletonDep
 
             foreach (var provider in providers)
             {
-                provider.Define(new SettingDefinitionContext(settings));
+                provider!.Define(new SettingDefinitionContext(settings));
             }
         }
 
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingEncryptionService.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingEncryptionService.cs
index 9f59f57910..45a3362d30 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingEncryptionService.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingEncryptionService.cs
@@ -17,7 +17,7 @@ public class SettingEncryptionService : ISettingEncryptionService, ITransientDep
         Logger = NullLogger<SettingEncryptionService>.Instance;
     }
 
-    public virtual string Encrypt(SettingDefinition settingDefinition, string plainValue)
+    public virtual string? Encrypt(SettingDefinition settingDefinition, string? plainValue)
     {
         if (plainValue.IsNullOrEmpty())
         {
@@ -27,7 +27,7 @@ public class SettingEncryptionService : ISettingEncryptionService, ITransientDep
         return StringEncryptionService.Encrypt(plainValue);
     }
 
-    public virtual string Decrypt(SettingDefinition settingDefinition, string encryptedValue)
+    public virtual string? Decrypt(SettingDefinition settingDefinition, string? encryptedValue)
     {
         if (encryptedValue.IsNullOrEmpty())
         {
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingProvider.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingProvider.cs
index 01791bef00..31dfecc4c0 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingProvider.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingProvider.cs
@@ -21,7 +21,7 @@ public class SettingProvider : ISettingProvider, ITransientDependency
         SettingValueProviderManager = settingValueProviderManager;
     }
 
-    public virtual async Task<string> GetOrNullAsync(string name)
+    public virtual async Task<string?> GetOrNullAsync(string name)
     {
         var setting = SettingDefinitionManager.Get(name);
         var providers = Enumerable
@@ -95,7 +95,7 @@ public class SettingProvider : ISettingProvider, ITransientDependency
         return settingValues;
     }
 
-    protected virtual async Task<string> GetOrNullValueFromProvidersAsync(
+    protected virtual async Task<string?> GetOrNullValueFromProvidersAsync(
         IEnumerable<ISettingValueProvider> providers,
         SettingDefinition setting)
     {
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValue.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValue.cs
index 63f6ab063f..56e972611b 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValue.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValue.cs
@@ -3,14 +3,14 @@
 namespace Volo.Abp.Settings;
 
 [Serializable]
-public class SettingValue : NameValue
+public class SettingValue : NameValue<string?>
 {
     public SettingValue()
     {
 
     }
 
-    public SettingValue(string name, string value)
+    public SettingValue(string name, string? value)
     {
         Name = name;
         Value = value;
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValueProvider.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValueProvider.cs
index c8b994986d..57d4b18a51 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValueProvider.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValueProvider.cs
@@ -15,7 +15,7 @@ public abstract class SettingValueProvider : ISettingValueProvider, ITransientDe
         SettingStore = settingStore;
     }
 
-    public abstract Task<string> GetOrNullAsync(SettingDefinition setting);
+    public abstract Task<string?> GetOrNullAsync(SettingDefinition setting);
 
     public abstract Task<List<SettingValue>> GetAllAsync(SettingDefinition[] settings);
 }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValueProviderManager.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValueProviderManager.cs
index f54b3cfda3..d0300357dc 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValueProviderManager.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingValueProviderManager.cs
@@ -24,7 +24,7 @@ public class SettingValueProviderManager : ISettingValueProviderManager, ISingle
             () => Options
                 .ValueProviders
                 .Select(type => serviceProvider.GetRequiredService(type) as ISettingValueProvider)
-                .ToList(),
+                .ToList()!,
             true
         );
     }
diff --git a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/UserSettingValueProvider.cs b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/UserSettingValueProvider.cs
index 791bef3709..7c1d65740a 100644
--- a/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/UserSettingValueProvider.cs
+++ b/framework/src/Volo.Abp.Settings/Volo/Abp/Settings/UserSettingValueProvider.cs
@@ -19,7 +19,7 @@ public class UserSettingValueProvider : SettingValueProvider
         CurrentUser = currentUser;
     }
 
-    public override async Task<string> GetOrNullAsync(SettingDefinition setting)
+    public override async Task<string?> GetOrNullAsync(SettingDefinition setting)
     {
         if (CurrentUser.Id == null)
         {