Support `Nullable` feature.

framework/src/Volo.Abp.Settings/Volo/Abp/Settings/IDynamicSettingDefinitionStore.cs

@@ -10,5 +10,5 @@ public interface IDynamicSettingDefinitionStore
 
     Task<IReadOnlyList<SettingDefinition>> GetAllAsync();
 
-    Task<SettingDefinition> GetOrNullAsync([NotNull] string name);
+    Task<SettingDefinition?> GetOrNullAsync([NotNull] string name);
 }

framework/src/Volo.Abp.Settings/Volo/Abp/Settings/ISettingDefinitionManager.cs

@@ -13,5 +13,5 @@ public interface ISettingDefinitionManager
     Task<IReadOnlyList<SettingDefinition>> GetAllAsync();
 
     [ItemCanBeNull]
-    Task<SettingDefinition> GetOrNullAsync([NotNull] string name);
+    Task<SettingDefinition?> GetOrNullAsync([NotNull] string name);
 }

framework/src/Volo.Abp.Settings/Volo/Abp/Settings/IStaticSettingDefinitionStore.cs

@@ -10,5 +10,5 @@ public interface IStaticSettingDefinitionStore
 
     Task<IReadOnlyList<SettingDefinition>> GetAllAsync();
 
-    Task<SettingDefinition> GetOrNullAsync([NotNull] string name);
+    Task<SettingDefinition?> GetOrNullAsync([NotNull] string name);
 }

framework/src/Volo.Abp.Settings/Volo/Abp/Settings/NullDynamicSettingDefinitionStore.cs

@@ -8,7 +8,8 @@ namespace Volo.Abp.Settings;
 
 public class NullDynamicSettingDefinitionStore : IDynamicSettingDefinitionStore, ISingletonDependency
 {
-    private readonly static Task<SettingDefinition> CachedSettingResult = Task.FromResult((SettingDefinition)null);
+    private readonly static Task<SettingDefinition?> CachedNullableSettingResult = Task.FromResult((SettingDefinition?)null);
+    private readonly static Task<SettingDefinition> CachedSettingResult = Task.FromResult((SettingDefinition)null!);
 
     private readonly static Task<IReadOnlyList<SettingDefinition>> CachedSettingsResult = Task.FromResult((IReadOnlyList<SettingDefinition>)Array.Empty<SettingDefinition>().ToImmutableList());
 
@@ -22,8 +23,8 @@ public class NullDynamicSettingDefinitionStore : IDynamicSettingDefinitionStore,
         return CachedSettingsResult;
     }
 
-    public Task<SettingDefinition> GetOrNullAsync(string name)
+    public Task<SettingDefinition?> GetOrNullAsync(string name)
     {
-        return CachedSettingResult;
+        return CachedNullableSettingResult;
     }
 }

framework/src/Volo.Abp.Settings/Volo/Abp/Settings/SettingDefinitionManager.cs

@@ -28,7 +28,7 @@ public class SettingDefinitionManager : ISettingDefinitionManager, ISingletonDep
         return permission;
     }
 
-    public virtual async Task<SettingDefinition> GetOrNullAsync(string name)
+    public virtual async Task<SettingDefinition?> GetOrNullAsync(string name)
     {
         Check.NotNull(name, nameof(name));
 

framework/src/Volo.Abp.Settings/Volo/Abp/Settings/StaticSettingDefinitionStore.cs

@@ -44,7 +44,7 @@ public class StaticSettingDefinitionStore : IStaticSettingDefinitionStore, ISing
         return Task.FromResult<IReadOnlyList<SettingDefinition>>(SettingDefinitions.Value.Values.ToImmutableList());
     }
 
-    public virtual Task<SettingDefinition> GetOrNullAsync(string name)
+    public virtual Task<SettingDefinition?> GetOrNullAsync(string name)
     {
         return Task.FromResult(SettingDefinitions.Value.GetOrDefault(name));
     }
@@ -62,7 +62,7 @@ public class StaticSettingDefinitionStore : IStaticSettingDefinitionStore, ISing
 
             foreach (var provider in providers)
             {
-                provider.Define(new SettingDefinitionContext(settings));
+                provider?.Define(new SettingDefinitionContext(settings));
             }
         }