diff --git a/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IDeletionAuditedObject.cs b/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IDeletionAuditedObject.cs
index a7be0c29a1..afec5e4e5f 100644
--- a/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IDeletionAuditedObject.cs
+++ b/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IDeletionAuditedObject.cs
@@ -22,5 +22,5 @@ public interface IDeletionAuditedObject<TUser> : IDeletionAuditedObject
     /// <summary>
     /// Reference to the deleter user.
     /// </summary>
-    TUser Deleter { get; }
+    TUser? Deleter { get; }
 }
diff --git a/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IMayHaveCreator.cs b/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IMayHaveCreator.cs
index 25748f5af9..78989e16d2 100644
--- a/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IMayHaveCreator.cs
+++ b/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IMayHaveCreator.cs
@@ -8,8 +8,7 @@ public interface IMayHaveCreator<TCreator>
     /// <summary>
     /// Reference to the creator.
     /// </summary>
-    [CanBeNull]
-    TCreator Creator { get; }
+    TCreator? Creator { get; }
 }
 
 /// <summary>
diff --git a/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IModificationAuditedObject.cs b/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IModificationAuditedObject.cs
index 48f26b6299..a82e1452e8 100644
--- a/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IModificationAuditedObject.cs
+++ b/framework/src/Volo.Abp.Auditing.Contracts/Volo/Abp/Auditing/IModificationAuditedObject.cs
@@ -22,5 +22,5 @@ public interface IModificationAuditedObject<TUser> : IModificationAuditedObject
     /// <summary>
     /// Reference to the last modifier user of this entity.
     /// </summary>
-    TUser LastModifier { get; }
+    TUser? LastModifier { get; }
 }
diff --git a/framework/src/Volo.Abp.BlazoriseUI/Components/ObjectExtending/LookupExtensionProperty.razor b/framework/src/Volo.Abp.BlazoriseUI/Components/ObjectExtending/LookupExtensionProperty.razor
index 7c32549d51..ecdae979f2 100644
--- a/framework/src/Volo.Abp.BlazoriseUI/Components/ObjectExtending/LookupExtensionProperty.razor
+++ b/framework/src/Volo.Abp.BlazoriseUI/Components/ObjectExtending/LookupExtensionProperty.razor
@@ -9,7 +9,7 @@
     <Autocomplete Data="@lookupItems"
                   TItem="SelectItem<object>"
                   TValue="object"
-                  TextField="item => item?.Text"
+                  TextField="item => item?.Text!"
                   ValueField="item => item?.Value"
                   SelectedValue="@SelectedValue"
                   SelectedValueChanged="@SelectedValueChanged"
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo.Abp.Ddd.Domain.csproj b/framework/src/Volo.Abp.Ddd.Domain/Volo.Abp.Ddd.Domain.csproj
index c15f7c96a8..5130c57f12 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo.Abp.Ddd.Domain.csproj
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo.Abp.Ddd.Domain.csproj
@@ -5,6 +5,8 @@
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;netstandard2.1;net7.0</TargetFrameworks>
+    <Nullable>enable</Nullable>
+    <WarningsAsErrors>Nullable</WarningsAsErrors>
     <AssemblyName>Volo.Abp.Ddd.Domain</AssemblyName>
     <PackageId>Volo.Abp.Ddd.Domain</PackageId>
     <AssetTargetFallback>$(AssetTargetFallback);portable-net45+win8+wp8+wpa81;</AssetTargetFallback>
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/AbpCommonDbContextRegistrationOptions.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/AbpCommonDbContextRegistrationOptions.cs
index bc50368645..8342451056 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/AbpCommonDbContextRegistrationOptions.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/AbpCommonDbContextRegistrationOptions.cs
@@ -16,13 +16,13 @@ public abstract class AbpCommonDbContextRegistrationOptions : IAbpCommonDbContex
 
     public IServiceCollection Services { get; }
 
-    public Dictionary<MultiTenantDbContextType, Type> ReplacedDbContextTypes { get; }
+    public Dictionary<MultiTenantDbContextType, Type?> ReplacedDbContextTypes { get; }
 
     public Type DefaultRepositoryDbContextType { get; protected set; }
 
-    public Type DefaultRepositoryImplementationType { get; private set; }
+    public Type? DefaultRepositoryImplementationType { get; private set; }
 
-    public Type DefaultRepositoryImplementationTypeWithoutKey { get; private set; }
+    public Type? DefaultRepositoryImplementationTypeWithoutKey { get; private set; }
 
     public bool RegisterDefaultRepositories { get; private set; }
 
@@ -40,7 +40,7 @@ public abstract class AbpCommonDbContextRegistrationOptions : IAbpCommonDbContex
         Services = services;
         DefaultRepositoryDbContextType = originalDbContextType;
         CustomRepositories = new Dictionary<Type, Type>();
-        ReplacedDbContextTypes = new Dictionary<MultiTenantDbContextType, Type>();
+        ReplacedDbContextTypes = new Dictionary<MultiTenantDbContextType, Type?>();
         SpecifiedDefaultRepositories = new List<Type>();
     }
 
@@ -54,7 +54,7 @@ public abstract class AbpCommonDbContextRegistrationOptions : IAbpCommonDbContex
         return ReplaceDbContext(typeof(TOtherDbContext), typeof(TTargetDbContext), multiTenancySides);
     }
 
-    public IAbpCommonDbContextRegistrationOptionsBuilder ReplaceDbContext(Type otherDbContextType, Type targetDbContextType = null, MultiTenancySides multiTenancySides = MultiTenancySides.Both)
+    public IAbpCommonDbContextRegistrationOptionsBuilder ReplaceDbContext(Type otherDbContextType, Type? targetDbContextType = null, MultiTenancySides multiTenancySides = MultiTenancySides.Both)
     {
         if (!otherDbContextType.IsAssignableFrom(OriginalDbContextType))
         {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/IAbpCommonDbContextRegistrationOptionsBuilder.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/IAbpCommonDbContextRegistrationOptionsBuilder.cs
index 58a82bf77d..ee580332a8 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/IAbpCommonDbContextRegistrationOptionsBuilder.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/IAbpCommonDbContextRegistrationOptionsBuilder.cs
@@ -90,5 +90,5 @@ public interface IAbpCommonDbContextRegistrationOptionsBuilder
     /// <param name="otherDbContextType">The DbContext type to be replaced</param>
     /// <param name="targetDbContextType">The target DbContext type (optional, used this DbContext type if not provided)</param>
     /// <param name="multiTenancySides">MultiTenancy side</param>
-    IAbpCommonDbContextRegistrationOptionsBuilder ReplaceDbContext(Type otherDbContextType, Type targetDbContextType = null, MultiTenancySides multiTenancySides = MultiTenancySides.Both);
+    IAbpCommonDbContextRegistrationOptionsBuilder ReplaceDbContext(Type otherDbContextType, Type? targetDbContextType = null, MultiTenancySides multiTenancySides = MultiTenancySides.Both);
 }
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/MultiTenantDbContextType.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/MultiTenantDbContextType.cs
index ff0d74608a..b015b9204a 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/MultiTenantDbContextType.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/DependencyInjection/MultiTenantDbContextType.cs
@@ -15,7 +15,7 @@ public class MultiTenantDbContextType
         MultiTenancySide = multiTenancySide;
     }
 
-    public override bool Equals(object obj)
+    public override bool Equals(object? obj)
     {
         var other = obj as MultiTenantDbContextType;
 
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/AuditedAggregateRootWithUser.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/AuditedAggregateRootWithUser.cs
index ebb573579b..f38c21d2fe 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/AuditedAggregateRootWithUser.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/AuditedAggregateRootWithUser.cs
@@ -12,10 +12,10 @@ public abstract class AuditedAggregateRootWithUser<TUser> : AuditedAggregateRoot
     where TUser : IEntity<Guid>
 {
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     /// <inheritdoc />
-    public virtual TUser LastModifier { get; set; }
+    public virtual TUser? LastModifier { get; set; }
 }
 
 /// <summary>
@@ -28,10 +28,10 @@ public abstract class AuditedAggregateRootWithUser<TKey, TUser> : AuditedAggrega
     where TUser : IEntity<Guid>
 {
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     /// <inheritdoc />
-    public virtual TUser LastModifier { get; set; }
+    public virtual TUser? LastModifier { get; set; }
 
     protected AuditedAggregateRootWithUser()
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/AuditedEntityWithUser.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/AuditedEntityWithUser.cs
index 99b9b66303..3f8598d348 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/AuditedEntityWithUser.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/AuditedEntityWithUser.cs
@@ -12,10 +12,10 @@ public abstract class AuditedEntityWithUser<TUser> : AuditedEntity, IAuditedObje
     where TUser : IEntity<Guid>
 {
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     /// <inheritdoc />
-    public virtual TUser LastModifier { get; set; }
+    public virtual TUser? LastModifier { get; set; }
 }
 
 /// <summary>
@@ -28,10 +28,10 @@ public abstract class AuditedEntityWithUser<TKey, TUser> : AuditedEntity<TKey>,
     where TUser : IEntity<Guid>
 {
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     /// <inheritdoc />
-    public virtual TUser LastModifier { get; set; }
+    public virtual TUser? LastModifier { get; set; }
 
     protected AuditedEntityWithUser()
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/CreationAuditedAggregateRootWithUser.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/CreationAuditedAggregateRootWithUser.cs
index 73da9d2026..4407a93de8 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/CreationAuditedAggregateRootWithUser.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/CreationAuditedAggregateRootWithUser.cs
@@ -11,7 +11,7 @@ namespace Volo.Abp.Domain.Entities.Auditing;
 public abstract class CreationAuditedAggregateRootWithUser<TUser> : CreationAuditedAggregateRoot, ICreationAuditedObject<TUser>
 {
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 }
 
 /// <summary>
@@ -23,7 +23,7 @@ public abstract class CreationAuditedAggregateRootWithUser<TUser> : CreationAudi
 public abstract class CreationAuditedAggregateRootWithUser<TKey, TUser> : CreationAuditedAggregateRoot<TKey>, ICreationAuditedObject<TUser>
 {
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     protected CreationAuditedAggregateRootWithUser()
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/CreationAuditedEntityWithUser.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/CreationAuditedEntityWithUser.cs
index 203967fb89..635bb06183 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/CreationAuditedEntityWithUser.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/CreationAuditedEntityWithUser.cs
@@ -11,7 +11,7 @@ namespace Volo.Abp.Domain.Entities.Auditing;
 public abstract class CreationAuditedEntityWithUser<TUser> : CreationAuditedEntity, ICreationAuditedObject<TUser>
 {
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 }
 
 /// <summary>
@@ -23,7 +23,7 @@ public abstract class CreationAuditedEntityWithUser<TUser> : CreationAuditedEnti
 public abstract class CreationAuditedEntityWithUser<TKey, TUser> : CreationAuditedEntity<TKey>, ICreationAuditedObject<TUser>
 {
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     protected CreationAuditedEntityWithUser()
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/FullAuditedAggregateRootWithUser.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/FullAuditedAggregateRootWithUser.cs
index 918270088e..af8f196f00 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/FullAuditedAggregateRootWithUser.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/FullAuditedAggregateRootWithUser.cs
@@ -12,13 +12,13 @@ public abstract class FullAuditedAggregateRootWithUser<TUser> : FullAuditedAggre
     where TUser : IEntity<Guid>
 {
     /// <inheritdoc />
-    public virtual TUser Deleter { get; set; }
+    public virtual TUser? Deleter { get; set; }
 
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     /// <inheritdoc />
-    public virtual TUser LastModifier { get; set; }
+    public virtual TUser? LastModifier { get; set; }
 }
 
 /// <summary>
@@ -31,13 +31,13 @@ public abstract class FullAuditedAggregateRootWithUser<TKey, TUser> : FullAudite
     where TUser : IEntity<Guid>
 {
     /// <inheritdoc />
-    public virtual TUser Deleter { get; set; }
+    public virtual TUser? Deleter { get; set; }
 
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     /// <inheritdoc />
-    public virtual TUser LastModifier { get; set; }
+    public virtual TUser? LastModifier { get; set; }
 
     protected FullAuditedAggregateRootWithUser()
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/FullAuditedEntityWithUser.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/FullAuditedEntityWithUser.cs
index 1f4886f4c0..834b106d95 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/FullAuditedEntityWithUser.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Auditing/FullAuditedEntityWithUser.cs
@@ -12,13 +12,13 @@ public abstract class FullAuditedEntityWithUser<TUser> : FullAuditedEntity, IFul
     where TUser : IEntity<Guid>
 {
     /// <inheritdoc />
-    public virtual TUser Deleter { get; set; }
+    public virtual TUser? Deleter { get; set; }
 
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     /// <inheritdoc />
-    public virtual TUser LastModifier { get; set; }
+    public virtual TUser? LastModifier { get; set; }
 }
 
 /// <summary>
@@ -31,13 +31,13 @@ public abstract class FullAuditedEntityWithUser<TKey, TUser> : FullAuditedEntity
     where TUser : IEntity<Guid>
 {
     /// <inheritdoc />
-    public virtual TUser Deleter { get; set; }
+    public virtual TUser? Deleter { get; set; }
 
     /// <inheritdoc />
-    public virtual TUser Creator { get; protected set; }
+    public virtual TUser? Creator { get; protected set; }
 
     /// <inheritdoc />
-    public virtual TUser LastModifier { get; set; }
+    public virtual TUser? LastModifier { get; set; }
 
     protected FullAuditedEntityWithUser()
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheBase.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheBase.cs
index 7e5b17b687..2cb2b2c32b 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheBase.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheBase.cs
@@ -27,23 +27,23 @@ public abstract class EntityCacheBase<TEntity, TEntityCacheItem, TKey> :
         UnitOfWorkManager = unitOfWorkManager;
     }
     
-    public virtual async Task<TEntityCacheItem> FindAsync(TKey id)
+    public virtual async Task<TEntityCacheItem?> FindAsync(TKey id)
     {
         return await Cache.GetOrAddAsync(
             id,
-            async () => MapToCacheItem(await Repository.FindAsync(id))
+            async () => MapToCacheItem(await Repository.FindAsync(id))!
         );
     }
 
     public virtual async Task<TEntityCacheItem> GetAsync(TKey id)
     {
-        return await Cache.GetOrAddAsync(
+        return (await Cache.GetOrAddAsync(
             id,
-            async () => MapToCacheItem(await Repository.GetAsync(id))
-        );
+            async () => MapToCacheItem(await Repository.GetAsync(id))!
+        ))!;
     }
 
-    protected abstract TEntityCacheItem MapToCacheItem(TEntity entity);
+    protected abstract TEntityCacheItem? MapToCacheItem(TEntity? entity);
     
     public async Task HandleEventAsync(EntityChangedEventData<TEntity> eventData)
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheServiceCollectionExtensions.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheServiceCollectionExtensions.cs
index bf7ceac45c..c208c7b107 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheServiceCollectionExtensions.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheServiceCollectionExtensions.cs
@@ -13,7 +13,7 @@ public static class EntityCacheServiceCollectionExtensions
 {
     public static IServiceCollection AddEntityCache<TEntity, TKey>(
         this IServiceCollection services,
-        [CanBeNull] DistributedCacheEntryOptions cacheOptions = null)
+        DistributedCacheEntryOptions? cacheOptions = null)
         where TEntity : Entity<TKey>
     {
         services
@@ -39,7 +39,7 @@ public static class EntityCacheServiceCollectionExtensions
 
     public static IServiceCollection AddEntityCache<TEntity, TEntityCacheItem, TKey>(
         this IServiceCollection services,
-        [CanBeNull] DistributedCacheEntryOptions cacheOptions = null)
+        DistributedCacheEntryOptions? cacheOptions = null)
         where TEntity : Entity<TKey>
         where TEntityCacheItem : class
     {
@@ -61,7 +61,7 @@ public static class EntityCacheServiceCollectionExtensions
 
     public static IServiceCollection AddEntityCache<TObjectMapperContext, TEntity, TEntityCacheItem, TKey>(
         this IServiceCollection services,
-        [CanBeNull] DistributedCacheEntryOptions cacheOptions = null)
+        DistributedCacheEntryOptions? cacheOptions = null)
         where TEntity : Entity<TKey>
         where TEntityCacheItem : class
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheWithObjectMapper.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheWithObjectMapper.cs
index 727df63ea7..a37ad49b1e 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheWithObjectMapper.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheWithObjectMapper.cs
@@ -23,7 +23,7 @@ public class EntityCacheWithObjectMapper<TEntity, TEntityCacheItem, TKey> :
         ObjectMapper = objectMapper;
     }
 
-    protected override TEntityCacheItem MapToCacheItem(TEntity entity)
+    protected override TEntityCacheItem? MapToCacheItem(TEntity? entity)
     {
         if (entity == null)
         {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheWithoutCacheItem.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheWithoutCacheItem.cs
index c81f3e5e9e..0f300a7f28 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheWithoutCacheItem.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/EntityCacheWithoutCacheItem.cs
@@ -16,7 +16,7 @@ public class EntityCacheWithoutCacheItem<TEntity, TKey> :
     {
     }
 
-    protected override TEntity MapToCacheItem(TEntity entity)
+    protected override TEntity? MapToCacheItem(TEntity? entity)
     {
         return entity;
     }
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/IEntityCache.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/IEntityCache.cs
index 84f4486c65..bd8ba80a63 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/IEntityCache.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Caching/IEntityCache.cs
@@ -10,8 +10,7 @@ public interface IEntityCache<TEntityCacheItem, in TKey>
     /// Gets the entity with given <paramref name="id"/>,
     /// or returns null if the entity was not found.
     /// </summary>
-    [ItemCanBeNull] 
-    Task<TEntityCacheItem> FindAsync(TKey id);
+    Task<TEntityCacheItem?> FindAsync(TKey id);
  
     /// <summary>
     /// Gets the entity with given <paramref name="id"/>,
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Entity.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Entity.cs
index 54ebd01d1e..9e52d1abfd 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Entity.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Entity.cs
@@ -18,7 +18,7 @@ public abstract class Entity : IEntity
         return $"[ENTITY: {GetType().Name}] Keys = {GetKeys().JoinAsString(", ")}";
     }
 
-    public abstract object[] GetKeys();
+    public abstract object?[] GetKeys();
 
     public bool EntityEquals(IEntity other)
     {
@@ -31,7 +31,7 @@ public abstract class Entity : IEntity
 public abstract class Entity<TKey> : Entity, IEntity<TKey>
 {
     /// <inheritdoc/>
-    public virtual TKey Id { get; protected set; }
+    public virtual TKey Id { get; protected set; } = default!;
 
     protected Entity()
     {
@@ -43,9 +43,9 @@ public abstract class Entity<TKey> : Entity, IEntity<TKey>
         Id = id;
     }
 
-    public override object[] GetKeys()
+    public override object?[] GetKeys()
     {
-        return new object[] { Id };
+        return new object?[] { Id };
     }
 
     /// <inheritdoc/>
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/EntityHelper.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/EntityHelper.cs
index f7a4f27e5f..584807fac5 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/EntityHelper.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/EntityHelper.cs
@@ -25,7 +25,7 @@ public static class EntityHelper
         return typeof(IMultiTenant).IsAssignableFrom(type);
     }
 
-    public static bool EntityEquals(IEntity entity1, IEntity entity2)
+    public static bool EntityEquals(IEntity? entity1, IEntity? entity2)
     {
         if (entity1 == null || entity2 == null)
         {
@@ -131,7 +131,7 @@ public static class EntityHelper
         return IsValueObjectPredicate(type);
     }
 
-    public static bool IsValueObject(object obj)
+    public static bool IsValueObject(object? obj)
     {
         return obj != null && IsValueObject(obj.GetType());
     }
@@ -161,7 +161,7 @@ public static class EntityHelper
 
     public static bool HasDefaultId<TKey>(IEntity<TKey> entity)
     {
-        if (EqualityComparer<TKey>.Default.Equals(entity.Id, default))
+        if (EqualityComparer<TKey>.Default.Equals(entity.Id, default!))
         {
             return true;
         }
@@ -180,7 +180,7 @@ public static class EntityHelper
         return false;
     }
 
-    private static bool IsDefaultKeyValue(object value)
+    private static bool IsDefaultKeyValue(object? value)
     {
         if (value == null)
         {
@@ -222,8 +222,7 @@ public static class EntityHelper
     /// Tries to find the primary key type of the given entity type.
     /// May return null if given type does not implement <see cref="IEntity{TKey}"/>
     /// </summary>
-    [CanBeNull]
-    public static Type FindPrimaryKeyType<TEntity>()
+    public static Type? FindPrimaryKeyType<TEntity>()
         where TEntity : IEntity
     {
         return FindPrimaryKeyType(typeof(TEntity));
@@ -233,8 +232,7 @@ public static class EntityHelper
     /// Tries to find the primary key type of the given entity type.
     /// May return null if given type does not implement <see cref="IEntity{TKey}"/>
     /// </summary>
-    [CanBeNull]
-    public static Type FindPrimaryKeyType([NotNull] Type entityType)
+    public static Type? FindPrimaryKeyType([NotNull] Type entityType)
     {
         if (!typeof(IEntity).IsAssignableFrom(entityType))
         {
@@ -260,7 +258,7 @@ public static class EntityHelper
         var lambdaParam = Expression.Parameter(typeof(TEntity));
         var leftExpression = Expression.PropertyOrField(lambdaParam, "Id");
         var idValue = Convert.ChangeType(id, typeof(TKey));
-        Expression<Func<object>> closure = () => idValue;
+        Expression<Func<object?>> closure = () => idValue;
         var rightExpression = Expression.Convert(closure.Body, leftExpression.Type);
         var lambdaBody = Expression.Equal(leftExpression, rightExpression);
         return Expression.Lambda<Func<TEntity, bool>>(lambdaBody, lambdaParam);
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntitySynchronizer.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntitySynchronizer.cs
index b971acc25f..5640c427c2 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntitySynchronizer.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntitySynchronizer.cs
@@ -22,7 +22,7 @@ public abstract class EntitySynchronizer<TEntity, TKey, TSourceEntityEto> :
         Repository = repository;
     }
 
-    protected override Task<TEntity> FindLocalEntityAsync(TSourceEntityEto eto)
+    protected override Task<TEntity?> FindLocalEntityAsync(TSourceEntityEto eto)
     {
         return Repository.FindAsync(eto.Id);
     }
@@ -154,10 +154,9 @@ public abstract class EntitySynchronizer<TEntity, TSourceEntityEto> :
         return true;
     }
 
-    [ItemCanBeNull]
-    protected abstract Task<TEntity> FindLocalEntityAsync(TSourceEntityEto eto);
+    protected abstract Task<TEntity?> FindLocalEntityAsync(TSourceEntityEto eto);
 
-    protected virtual Task<bool> IsEtoNewerAsync(TSourceEntityEto eto, [CanBeNull] TEntity localEntity)
+    protected virtual Task<bool> IsEtoNewerAsync(TSourceEntityEto eto, TEntity? localEntity)
     {
         if (localEntity is IHasEntityVersion versionedLocalEntity && eto is IHasEntityVersion versionedEto)
         {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntityToEtoMapper.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntityToEtoMapper.cs
index b9d5911375..1710fe81e3 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntityToEtoMapper.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntityToEtoMapper.cs
@@ -21,7 +21,7 @@ public class EntityToEtoMapper : IEntityToEtoMapper, ITransientDependency
         Options = options.Value;
     }
 
-    public object Map(object entityObj)
+    public object? Map(object entityObj)
     {
         Check.NotNull(entityObj, nameof(entityObj));
 
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/EntityChangeEventHelper.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/EntityChangeEventHelper.cs
index 20556f16ff..44eb5c058a 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/EntityChangeEventHelper.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/EntityChangeEventHelper.cs
@@ -133,7 +133,7 @@ public class EntityChangeEventHelper : IEntityChangeEventHelper, ITransientDepen
     {
         var entityType = ProxyHelper.UnProxy(entityOrEto).GetType();
         var eventType = genericEventType.MakeGenericType(entityType);
-        var eventData = Activator.CreateInstance(eventType, entityOrEto);
+        var eventData = Activator.CreateInstance(eventType, entityOrEto)!;
         var currentUow = UnitOfWorkManager.Current;
 
         if (currentUow == null)
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/EntityEventData.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/EntityEventData.cs
index c2845da60e..b295f22f4e 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/EntityEventData.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/EntityEventData.cs
@@ -27,7 +27,7 @@ public class EntityEventData<TEntity> : IEventDataWithInheritableGenericArgument
 
     public virtual object[] GetConstructorArgs()
     {
-        return new object[] { Entity };
+        return new object[] { Entity! };
     }
 
     public virtual bool IsMultiTenant(out Guid? tenantId)
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/IEntity.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/IEntity.cs
index 7f4d425df2..1df1b75696 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/IEntity.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/IEntity.cs
@@ -10,7 +10,7 @@ public interface IEntity
     /// Returns an array of ordered keys for this entity.
     /// </summary>
     /// <returns></returns>
-    object[] GetKeys();
+    object?[] GetKeys();
 }
 
 /// <summary>
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/BasicRepositoryBase.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/BasicRepositoryBase.cs
index 8a87f9c391..0d86045eea 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/BasicRepositoryBase.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/BasicRepositoryBase.cs
@@ -20,9 +20,9 @@ public abstract class BasicRepositoryBase<TEntity> :
     IUnitOfWorkEnabled
     where TEntity : class, IEntity
 {
-    public IAbpLazyServiceProvider LazyServiceProvider { get; set; }
+    public IAbpLazyServiceProvider LazyServiceProvider { get; set; } = default!;
 
-    public IServiceProvider ServiceProvider { get; set; }
+    public IServiceProvider ServiceProvider { get; set; } = default!;
 
     public IDataFilter DataFilter => LazyServiceProvider.LazyGetRequiredService<IDataFilter>();
 
@@ -123,7 +123,7 @@ public abstract class BasicRepositoryBase<TEntity, TKey> : BasicRepositoryBase<T
         return entity;
     }
 
-    public abstract Task<TEntity> FindAsync(TKey id, bool includeDetails = true, CancellationToken cancellationToken = default);
+    public abstract Task<TEntity?> FindAsync(TKey id, bool includeDetails = true, CancellationToken cancellationToken = default);
 
     public virtual async Task DeleteAsync(TKey id, bool autoSave = false, CancellationToken cancellationToken = default)
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/IReadOnlyBasicRepository.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/IReadOnlyBasicRepository.cs
index 6d447552f9..0736685709 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/IReadOnlyBasicRepository.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/IReadOnlyBasicRepository.cs
@@ -51,5 +51,5 @@ public interface IReadOnlyBasicRepository<TEntity, TKey> : IReadOnlyBasicReposit
     /// <param name="includeDetails">Set true to include all children of this entity</param>
     /// <param name="cancellationToken">A <see cref="T:System.Threading.CancellationToken" /> to observe while waiting for the task to complete.</param>
     /// <returns>Entity or null</returns>
-    Task<TEntity> FindAsync(TKey id, bool includeDetails = true, CancellationToken cancellationToken = default);
+    Task<TEntity?> FindAsync(TKey id, bool includeDetails = true, CancellationToken cancellationToken = default);
 }
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/IRepository.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/IRepository.cs
index da915626a8..3c7ae81875 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/IRepository.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/IRepository.cs
@@ -28,7 +28,7 @@ public interface IRepository<TEntity> : IReadOnlyRepository<TEntity>, IBasicRepo
     /// <param name="predicate">A condition to find the entity</param>
     /// <param name="includeDetails">Set true to include all children of this entity</param>
     /// <param name="cancellationToken">A <see cref="T:System.Threading.CancellationToken" /> to observe while waiting for the task to complete.</param>
-    Task<TEntity> FindAsync(
+    Task<TEntity?> FindAsync(
         [NotNull] Expression<Func<TEntity, bool>> predicate,
         bool includeDetails = true,
         CancellationToken cancellationToken = default
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryAsyncExtensions.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryAsyncExtensions.cs
index 304f9ea0bd..2115d00200 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryAsyncExtensions.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryAsyncExtensions.cs
@@ -120,7 +120,7 @@ public static class RepositoryAsyncExtensions
         return await repository.AsyncExecuter.FirstAsync(queryable, predicate, cancellationToken);
     }
 
-    public static async Task<T> FirstOrDefaultAsync<T>(
+    public static async Task<T?> FirstOrDefaultAsync<T>(
         [NotNull] this IReadOnlyRepository<T> repository,
         CancellationToken cancellationToken = default)
         where T : class, IEntity
@@ -129,7 +129,7 @@ public static class RepositoryAsyncExtensions
         return await repository.AsyncExecuter.FirstOrDefaultAsync(queryable, cancellationToken);
     }
 
-    public static async Task<T> FirstOrDefaultAsync<T>(
+    public static async Task<T?> FirstOrDefaultAsync<T>(
         [NotNull] this IReadOnlyRepository<T> repository,
         [NotNull] Expression<Func<T, bool>> predicate,
         CancellationToken cancellationToken = default)
@@ -162,7 +162,7 @@ public static class RepositoryAsyncExtensions
         return await repository.AsyncExecuter.LastAsync(queryable, predicate, cancellationToken);
     }
 
-    public static async Task<T> LastOrDefaultAsync<T>(
+    public static async Task<T?> LastOrDefaultAsync<T>(
         [NotNull] this IReadOnlyRepository<T> repository,
         CancellationToken cancellationToken = default)
         where T : class, IEntity
@@ -171,7 +171,7 @@ public static class RepositoryAsyncExtensions
         return await repository.AsyncExecuter.LastOrDefaultAsync(queryable, cancellationToken);
     }
 
-    public static async Task<T> LastOrDefaultAsync<T>(
+    public static async Task<T?> LastOrDefaultAsync<T>(
         [NotNull] this IReadOnlyRepository<T> repository,
         [NotNull] Expression<Func<T, bool>> predicate,
         CancellationToken cancellationToken = default)
@@ -204,7 +204,7 @@ public static class RepositoryAsyncExtensions
         return await repository.AsyncExecuter.SingleAsync(queryable, predicate, cancellationToken);
     }
 
-    public static async Task<T> SingleOrDefaultAsync<T>(
+    public static async Task<T?> SingleOrDefaultAsync<T>(
         [NotNull] this IReadOnlyRepository<T> repository,
         CancellationToken cancellationToken = default)
         where T : class, IEntity
@@ -213,7 +213,7 @@ public static class RepositoryAsyncExtensions
         return await repository.AsyncExecuter.SingleOrDefaultAsync(queryable, cancellationToken);
     }
 
-    public static async Task<T> SingleOrDefaultAsync<T>(
+    public static async Task<T?> SingleOrDefaultAsync<T>(
         [NotNull] this IReadOnlyRepository<T> repository,
         [NotNull] Expression<Func<T, bool>> predicate,
         CancellationToken cancellationToken = default)
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryBase.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryBase.cs
index d843584fc4..eb2457f8c8 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryBase.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryBase.cs
@@ -41,7 +41,7 @@ public abstract class RepositoryBase<TEntity> : BasicRepositoryBase<TEntity>, IR
 
     public abstract Task<IQueryable<TEntity>> GetQueryableAsync();
 
-    public abstract Task<TEntity> FindAsync(
+    public abstract Task<TEntity?> FindAsync(
         Expression<Func<TEntity, bool>> predicate,
         bool includeDetails = true,
         CancellationToken cancellationToken = default);
@@ -76,13 +76,13 @@ public abstract class RepositoryBase<TEntity> : BasicRepositoryBase<TEntity>, IR
     {
         if (typeof(ISoftDelete).IsAssignableFrom(typeof(TOtherEntity)))
         {
-            query = (TQueryable)query.WhereIf(DataFilter.IsEnabled<ISoftDelete>(), e => ((ISoftDelete)e).IsDeleted == false);
+            query = (TQueryable)query.WhereIf(DataFilter.IsEnabled<ISoftDelete>(), e => ((ISoftDelete)e!).IsDeleted == false);
         }
 
         if (typeof(IMultiTenant).IsAssignableFrom(typeof(TOtherEntity)))
         {
             var tenantId = CurrentTenant.Id;
-            query = (TQueryable)query.WhereIf(DataFilter.IsEnabled<IMultiTenant>(), e => ((IMultiTenant)e).TenantId == tenantId);
+            query = (TQueryable)query.WhereIf(DataFilter.IsEnabled<IMultiTenant>(), e => ((IMultiTenant)e!).TenantId == tenantId);
         }
 
         return query;
@@ -94,7 +94,7 @@ public abstract class RepositoryBase<TEntity, TKey> : RepositoryBase<TEntity>, I
 {
     public abstract Task<TEntity> GetAsync(TKey id, bool includeDetails = true, CancellationToken cancellationToken = default);
 
-    public abstract Task<TEntity> FindAsync(TKey id, bool includeDetails = true, CancellationToken cancellationToken = default);
+    public abstract Task<TEntity?> FindAsync(TKey id, bool includeDetails = true, CancellationToken cancellationToken = default);
 
     public virtual async Task DeleteAsync(TKey id, bool autoSave = false, CancellationToken cancellationToken = default)
     {
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryExtensions.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryExtensions.cs
index 379203f46a..cbebf62196 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryExtensions.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryExtensions.cs
@@ -54,7 +54,7 @@ public static class RepositoryExtensions
     )
        where TEntity : class, IEntity<TKey>
     {
-        if (!await repository.AnyAsync(x => x.Id.Equals(id), cancellationToken))
+        if (!await repository.AnyAsync(x => x.Id!.Equals(id), cancellationToken))
         {
             throw new EntityNotFoundException(typeof(TEntity), id);
         }
@@ -87,7 +87,7 @@ public static class RepositoryExtensions
         {
             using (var uow = uowManager.Begin())
             {
-                await HardDeleteWithUnitOfWorkAsync(repository, predicate, autoSave, cancellationToken, uowManager.Current);
+                await HardDeleteWithUnitOfWorkAsync(repository, predicate, autoSave, cancellationToken, uowManager.Current!);
                 await uow.CompleteAsync(cancellationToken);
             }
         }
@@ -111,7 +111,7 @@ public static class RepositoryExtensions
         {
             using (var uow = uowManager.Begin())
             {
-                await HardDeleteWithUnitOfWorkAsync(repository, entities, autoSave, cancellationToken, uowManager.Current);
+                await HardDeleteWithUnitOfWorkAsync(repository, entities, autoSave, cancellationToken, uowManager.Current!);
                 await uow.CompleteAsync(cancellationToken);
             }
         }
@@ -135,7 +135,7 @@ public static class RepositoryExtensions
         {
             using (var uow = uowManager.Begin())
             {
-                await HardDeleteWithUnitOfWorkAsync(repository, entity, autoSave, cancellationToken, uowManager.Current);
+                await HardDeleteWithUnitOfWorkAsync(repository, entity, autoSave, cancellationToken, uowManager.Current!);
                 await uow.CompleteAsync(cancellationToken);
             }
         }
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryRegistrarBase.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryRegistrarBase.cs
index 320aed8312..d162f2ffea 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryRegistrarBase.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Repositories/RepositoryRegistrarBase.cs
@@ -75,12 +75,12 @@ public abstract class RepositoryRegistrarBase<TOptions>
         if (primaryKeyType == null)
         {
             return Options.SpecifiedDefaultRepositoryTypes
-                ? Options.DefaultRepositoryImplementationTypeWithoutKey.MakeGenericType(entityType)
+                ? Options.DefaultRepositoryImplementationTypeWithoutKey!.MakeGenericType(entityType)
                 : GetRepositoryType(Options.DefaultRepositoryDbContextType, entityType);
         }
 
         return Options.SpecifiedDefaultRepositoryTypes
-            ? Options.DefaultRepositoryImplementationType.MakeGenericType(entityType, primaryKeyType)
+            ? Options.DefaultRepositoryImplementationType!.MakeGenericType(entityType, primaryKeyType)
             : GetRepositoryType(Options.DefaultRepositoryDbContextType, entityType, primaryKeyType);
     }
 
diff --git a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Services/DomainService.cs b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Services/DomainService.cs
index 32cf42409c..b36b32eafd 100644
--- a/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Services/DomainService.cs
+++ b/framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Services/DomainService.cs
@@ -11,10 +11,10 @@ namespace Volo.Abp.Domain.Services;
 
 public abstract class DomainService : IDomainService
 {
-    public IAbpLazyServiceProvider LazyServiceProvider { get; set; }
+    public IAbpLazyServiceProvider LazyServiceProvider { get; set; } = default!;
 
     [Obsolete("Use LazyServiceProvider instead.")]
-    public IServiceProvider ServiceProvider { get; set; }
+    public IServiceProvider ServiceProvider { get; set; } = default!;
 
     protected IClock Clock => LazyServiceProvider.LazyGetRequiredService<IClock>();
 
@@ -26,5 +26,5 @@ public abstract class DomainService : IDomainService
 
     protected IAsyncQueryableExecuter AsyncExecuter => LazyServiceProvider.LazyGetRequiredService<IAsyncQueryableExecuter>();
 
-    protected ILogger Logger => LazyServiceProvider.LazyGetService<ILogger>(provider => LoggerFactory?.CreateLogger(GetType().FullName) ?? NullLogger.Instance);
+    protected ILogger Logger => LazyServiceProvider.LazyGetService<ILogger>(provider => LoggerFactory?.CreateLogger(GetType().FullName!) ?? NullLogger.Instance);
 }
diff --git a/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/AsyncQueryableExecuter.cs b/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/AsyncQueryableExecuter.cs
index 108d3bb595..a6b9fb7949 100644
--- a/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/AsyncQueryableExecuter.cs
+++ b/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/AsyncQueryableExecuter.cs
@@ -209,7 +209,7 @@ public class AsyncQueryableExecuter : IAsyncQueryableExecuter, ISingletonDepende
         return Task.FromResult(queryable.SingleOrDefault(predicate))!;
     }
 
-    public Task<T?> MinAsync<T>(IQueryable<T> queryable, CancellationToken cancellationToken = default)
+    public Task<T> MinAsync<T>(IQueryable<T> queryable, CancellationToken cancellationToken = default)
     {
         var provider = FindProvider(queryable);
         
@@ -221,7 +221,7 @@ public class AsyncQueryableExecuter : IAsyncQueryableExecuter, ISingletonDepende
         return Task.FromResult(queryable.Min())!;
     }
 
-    public Task<TResult?> MinAsync<T, TResult>(IQueryable<T> queryable, Expression<Func<T, TResult>> selector, CancellationToken cancellationToken = default)
+    public Task<TResult> MinAsync<T, TResult>(IQueryable<T> queryable, Expression<Func<T, TResult>> selector, CancellationToken cancellationToken = default)
     {
         var provider = FindProvider(queryable);
         
@@ -233,7 +233,7 @@ public class AsyncQueryableExecuter : IAsyncQueryableExecuter, ISingletonDepende
         return Task.FromResult(queryable.Min(selector))!;
     }
 
-    public Task<T?> MaxAsync<T>(IQueryable<T> queryable, CancellationToken cancellationToken = default)
+    public Task<T> MaxAsync<T>(IQueryable<T> queryable, CancellationToken cancellationToken = default)
     {
         var provider = FindProvider(queryable);
         
@@ -245,7 +245,7 @@ public class AsyncQueryableExecuter : IAsyncQueryableExecuter, ISingletonDepende
         return Task.FromResult(queryable.Max())!;
     }
 
-    public Task<TResult?> MaxAsync<T, TResult>(IQueryable<T> queryable, Expression<Func<T, TResult>> selector, CancellationToken cancellationToken = default)
+    public Task<TResult> MaxAsync<T, TResult>(IQueryable<T> queryable, Expression<Func<T, TResult>> selector, CancellationToken cancellationToken = default)
     {
         var provider = FindProvider(queryable);
         
diff --git a/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/IAsyncQueryableExecuter.cs b/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/IAsyncQueryableExecuter.cs
index 2bea6c4604..4ee0666f4c 100644
--- a/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/IAsyncQueryableExecuter.cs
+++ b/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/IAsyncQueryableExecuter.cs
@@ -137,12 +137,12 @@ public interface IAsyncQueryableExecuter
 
     #region Min
 
-    Task<T?> MinAsync<T>(
+    Task<T> MinAsync<T>(
         [NotNull] IQueryable<T> queryable,
         CancellationToken cancellationToken = default);
 
 
-    Task<TResult?> MinAsync<T, TResult>(
+    Task<TResult> MinAsync<T, TResult>(
         [NotNull] IQueryable<T> queryable,
         [NotNull] Expression<Func<T, TResult>> selector,
         CancellationToken cancellationToken = default);
@@ -151,12 +151,12 @@ public interface IAsyncQueryableExecuter
 
     #region Max
 
-    Task<T?> MaxAsync<T>(
+    Task<T> MaxAsync<T>(
         [NotNull] IQueryable<T> queryable,
         CancellationToken cancellationToken = default);
 
 
-    Task<TResult?> MaxAsync<T, TResult>(
+    Task<TResult> MaxAsync<T, TResult>(
         [NotNull] IQueryable<T> queryable,
         [NotNull] Expression<Func<T, TResult>> selector,
         CancellationToken cancellationToken = default);
diff --git a/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/IAsyncQueryableProvider.cs b/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/IAsyncQueryableProvider.cs
index 3f38553ac5..3239fde6d6 100644
--- a/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/IAsyncQueryableProvider.cs
+++ b/framework/src/Volo.Abp.Threading/Volo/Abp/Linq/IAsyncQueryableProvider.cs
@@ -139,12 +139,12 @@ public interface IAsyncQueryableProvider
 
     #region Min
 
-    Task<T?> MinAsync<T>(
+    Task<T> MinAsync<T>(
         [NotNull] IQueryable<T> queryable,
         CancellationToken cancellationToken = default);
 
 
-    Task<TResult?> MinAsync<T, TResult>(
+    Task<TResult> MinAsync<T, TResult>(
         [NotNull] IQueryable<T> queryable,
         [NotNull] Expression<Func<T, TResult>> selector,
         CancellationToken cancellationToken = default);
@@ -153,12 +153,12 @@ public interface IAsyncQueryableProvider
 
     #region Max
 
-    Task<T?> MaxAsync<T>(
+    Task<T> MaxAsync<T>(
         [NotNull] IQueryable<T> queryable,
         CancellationToken cancellationToken = default);
 
 
-    Task<TResult?> MaxAsync<T, TResult>(
+    Task<TResult> MaxAsync<T, TResult>(
         [NotNull] IQueryable<T> queryable,
         [NotNull] Expression<Func<T, TResult>> selector,
         CancellationToken cancellationToken = default);