diff --git a/framework/src/Volo.Abp.Localization/Volo.Abp.Localization.csproj b/framework/src/Volo.Abp.Localization/Volo.Abp.Localization.csproj
index 8b889e2057..f4c5c4ece2 100644
--- a/framework/src/Volo.Abp.Localization/Volo.Abp.Localization.csproj
+++ b/framework/src/Volo.Abp.Localization/Volo.Abp.Localization.csproj
@@ -5,6 +5,8 @@
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;netstandard2.1;net7.0</TargetFrameworks>
+    <Nullable>enable</Nullable>
+    <WarningsAsErrors>Nullable</WarningsAsErrors>
     <AssemblyName>Volo.Abp.Localization</AssemblyName>
     <PackageId>Volo.Abp.Localization</PackageId>
     <AssetTargetFallback>$(AssetTargetFallback);portable-net45+win8+wp8+wpa81;</AssetTargetFallback>
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpDictionaryBasedStringLocalizer.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpDictionaryBasedStringLocalizer.cs
index cf5c1ebb82..86133cdf17 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpDictionaryBasedStringLocalizer.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpDictionaryBasedStringLocalizer.cs
@@ -118,7 +118,7 @@ public class AbpDictionaryBasedStringLocalizer : IAbpStringLocalizer
         return value;
     }
 
-    protected virtual LocalizedString GetLocalizedStringOrNull(
+    protected virtual LocalizedString? GetLocalizedStringOrNull(
         string name,
         string cultureName,
         bool tryDefaults = true)
@@ -153,7 +153,7 @@ public class AbpDictionaryBasedStringLocalizer : IAbpStringLocalizer
             //Try to get from default language
             if (!Resource.DefaultCultureName.IsNullOrEmpty())
             {
-                var strDefault = Resource.Contributors.GetOrNull(Resource.DefaultCultureName, name);
+                var strDefault = Resource.Contributors.GetOrNull(Resource.DefaultCultureName!, name);
                 if (strDefault != null)
                 {
                     return strDefault;
@@ -208,7 +208,7 @@ public class AbpDictionaryBasedStringLocalizer : IAbpStringLocalizer
             //Fill all strings from default culture
             if (!Resource.DefaultCultureName.IsNullOrEmpty())
             {
-                Resource.Contributors.Fill(Resource.DefaultCultureName, allStrings, includeDynamicContributors);
+                Resource.Contributors.Fill(Resource.DefaultCultureName!, allStrings, includeDynamicContributors);
             }
 
             //Overwrite all strings from the language based on country culture
@@ -268,7 +268,7 @@ public class AbpDictionaryBasedStringLocalizer : IAbpStringLocalizer
             if (!Resource.DefaultCultureName.IsNullOrEmpty())
             {
                 await Resource.Contributors.FillAsync(
-                    Resource.DefaultCultureName,
+                    Resource.DefaultCultureName!,
                     allStrings,
                     includeDynamicContributors
                 );
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpEnumLocalizer.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpEnumLocalizer.cs
index 3fc053da6a..b2acb3d072 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpEnumLocalizer.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpEnumLocalizer.cs
@@ -19,14 +19,14 @@ public class AbpEnumLocalizer : IAbpEnumLocalizer, ITransientDependency
         return GetStringInternal(enumType, enumValue, StringLocalizerFactory.CreateDefaultOrNull());
     }
 
-    public virtual string GetString(Type enumType, object enumValue, params IStringLocalizer[] specifyLocalizers)
+    public virtual string GetString(Type enumType, object enumValue, params IStringLocalizer?[] specifyLocalizers)
     {
         return GetStringInternal(enumType, enumValue, specifyLocalizers);
     }
 
-    protected virtual string GetStringInternal(Type enumType, object enumValue, params IStringLocalizer[] specifyLocalizers)
+    protected virtual string GetStringInternal(Type enumType, object enumValue, params IStringLocalizer?[] specifyLocalizers)
     {
-        var memberName = enumType.GetEnumName(enumValue);
+        var memberName = enumType.GetEnumName(enumValue)!;
         var localizedString = GetStringOrNull(
             specifyLocalizers,
             new[]
@@ -42,7 +42,7 @@ public class AbpEnumLocalizer : IAbpEnumLocalizer, ITransientDependency
         return localizedString ?? memberName;
     }
 
-    protected virtual string GetStringOrNull(IStringLocalizer[] localizers, IEnumerable<string> keys)
+    protected virtual string? GetStringOrNull(IStringLocalizer?[] localizers, IEnumerable<string> keys)
     {
         foreach (var key in keys)
         {
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpLocalizationOptions.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpLocalizationOptions.cs
index 5228f886e9..0fd9d47ac8 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpLocalizationOptions.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpLocalizationOptions.cs
@@ -11,7 +11,7 @@ public class AbpLocalizationOptions
     /// <summary>
     /// Used as the default resource when resource was not specified on a localization operation.
     /// </summary>
-    public Type DefaultResourceType { get; set; }
+    public Type? DefaultResourceType { get; set; }
 
     public ITypeList<ILocalizationResourceContributor> GlobalContributors { get; }
 
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpStringLocalizerExtensions.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpStringLocalizerExtensions.cs
index 9b3bb2c201..91c7126a97 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpStringLocalizerExtensions.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpStringLocalizerExtensions.cs
@@ -35,7 +35,7 @@ public static class AbpStringLocalizerExtensions
             throw new AbpException($"Could not find the _localizer field inside the {typeof(StringLocalizer<>).FullName} class. Probably its name has changed. Please report this issue to the ABP framework.");
         }
 
-        return localizerField.GetValue(stringLocalizer) as IStringLocalizer;
+        return (localizerField.GetValue(stringLocalizer) as IStringLocalizer)!;
     }
 
     public static IEnumerable<LocalizedString> GetAllStrings(
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpStringLocalizerFactory.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpStringLocalizerFactory.cs
index b89a54abd9..f40385c128 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpStringLocalizerFactory.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/AbpStringLocalizerFactory.cs
@@ -52,12 +52,12 @@ public class AbpStringLocalizerFactory : IStringLocalizerFactory, IAbpStringLoca
         return CreateInternal(resource.ResourceName, resource, lockCache);
     }
     
-    public IStringLocalizer CreateByResourceNameOrNull(string resourceName)
+    public IStringLocalizer? CreateByResourceNameOrNull(string resourceName)
     {
         return CreateByResourceNameOrNullInternal(resourceName, lockCache: true);
     }
     
-    private IStringLocalizer CreateByResourceNameOrNullInternal(
+    private IStringLocalizer? CreateByResourceNameOrNullInternal(
         string resourceName,
         bool lockCache)
     {
@@ -74,12 +74,12 @@ public class AbpStringLocalizerFactory : IStringLocalizerFactory, IAbpStringLoca
         return CreateInternal(resourceName, resource, lockCache);
     }
 
-    public Task<IStringLocalizer> CreateByResourceNameOrNullAsync(string resourceName)
+    public Task<IStringLocalizer?> CreateByResourceNameOrNullAsync(string resourceName)
     {
         return CreateByResourceNameOrNullInternalAsync(resourceName, lockCache: true);
     }
     
-    private async Task<IStringLocalizer> CreateByResourceNameOrNullInternalAsync(
+    private async Task<IStringLocalizer?> CreateByResourceNameOrNullInternalAsync(
         string resourceName,
         bool lockCache)
     {
@@ -175,7 +175,7 @@ public class AbpStringLocalizerFactory : IStringLocalizerFactory, IAbpStringLoca
         {
             resource.Contributors.Add(
                 Activator
-                    .CreateInstance(globalContributorType)
+                    .CreateInstance(globalContributorType)!
                     .As<ILocalizationResourceContributor>()
             );
         }
@@ -194,7 +194,7 @@ public class AbpStringLocalizerFactory : IStringLocalizerFactory, IAbpStringLoca
                     .BaseResourceNames
                     .Select(x => CreateByResourceNameOrNullInternal(x, lockCache: false))
                     .Where(x => x != null)
-                    .ToList(),
+                    .ToList()!,
                 AbpLocalizationOptions
             )
         );
@@ -206,7 +206,7 @@ public class AbpStringLocalizerFactory : IStringLocalizerFactory, IAbpStringLoca
         {
             resource.Contributors.Add(
                 Activator
-                    .CreateInstance(globalContributorType)
+                    .CreateInstance(globalContributorType)!
                     .As<ILocalizationResourceContributor>()
             );
         }
@@ -259,7 +259,7 @@ public class AbpStringLocalizerFactory : IStringLocalizerFactory, IAbpStringLoca
         }
     }
 
-    public IStringLocalizer CreateDefaultOrNull()
+    public IStringLocalizer? CreateDefaultOrNull()
     {
         if (AbpLocalizationOptions.DefaultResourceType == null)
         {
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/External/IExternalLocalizationStore.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/External/IExternalLocalizationStore.cs
index cd48bb1bd9..c2aa55cd2f 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/External/IExternalLocalizationStore.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/External/IExternalLocalizationStore.cs
@@ -5,11 +5,9 @@ namespace Volo.Abp.Localization.External;
 
 public interface IExternalLocalizationStore
 {
-    [CanBeNull] 
-    LocalizationResourceBase GetResourceOrNull([NotNull] string resourceName);
+    LocalizationResourceBase? GetResourceOrNull([NotNull] string resourceName);
     
-    [ItemCanBeNull] 
-    Task<LocalizationResourceBase> GetResourceOrNullAsync([NotNull] string resourceName);
+    Task<LocalizationResourceBase?> GetResourceOrNullAsync([NotNull] string resourceName);
     
     Task<string[]> GetResourceNamesAsync();
     
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/External/NullExternalLocalizationStore.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/External/NullExternalLocalizationStore.cs
index 508f947981..891beba134 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/External/NullExternalLocalizationStore.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/External/NullExternalLocalizationStore.cs
@@ -6,14 +6,14 @@ namespace Volo.Abp.Localization.External;
 
 public class NullExternalLocalizationStore : IExternalLocalizationStore, ISingletonDependency
 {
-    public LocalizationResourceBase GetResourceOrNull(string resourceName)
+    public LocalizationResourceBase? GetResourceOrNull(string resourceName)
     {
         return null;
     }
 
-    public Task<LocalizationResourceBase> GetResourceOrNullAsync(string resourceName)
+    public Task<LocalizationResourceBase?> GetResourceOrNullAsync(string resourceName)
     {
-        return Task.FromResult<LocalizationResourceBase>(null);
+        return Task.FromResult<LocalizationResourceBase?>(null);
     }
 
     public Task<string[]> GetResourceNamesAsync()
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILanguageInfo.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILanguageInfo.cs
index d4e06e9af5..e8ae6935de 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILanguageInfo.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILanguageInfo.cs
@@ -8,5 +8,5 @@ public interface ILanguageInfo
 
     string DisplayName { get; }
 
-    string FlagIcon { get; }
+    string? FlagIcon { get; }
 }
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizableStringSerializer.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizableStringSerializer.cs
index 6f7a487b6c..7d068b9494 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizableStringSerializer.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizableStringSerializer.cs
@@ -2,7 +2,7 @@
 
 public interface ILocalizableStringSerializer
 {
-    string Serialize(ILocalizableString localizableString);
+    string? Serialize(ILocalizableString localizableString);
     
     ILocalizableString Deserialize(string value);
 }
\ No newline at end of file
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizationDictionary.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizationDictionary.cs
index d5fcab206b..e6879c0007 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizationDictionary.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizationDictionary.cs
@@ -10,7 +10,7 @@ public interface ILocalizationDictionary
 {
     string CultureName { get; }
 
-    LocalizedString GetOrNull(string name);
+    LocalizedString? GetOrNull(string name);
 
     void Fill(Dictionary<string, LocalizedString> dictionary);
 }
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizationResourceContributor.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizationResourceContributor.cs
index 2a79d20821..2d3ade519f 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizationResourceContributor.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/ILocalizationResourceContributor.cs
@@ -10,7 +10,7 @@ public interface ILocalizationResourceContributor
     
     void Initialize(LocalizationResourceInitializationContext context);
 
-    LocalizedString GetOrNull(string cultureName, string name);
+    LocalizedString? GetOrNull(string cultureName, string name);
 
     void Fill(string cultureName, Dictionary<string, LocalizedString> dictionary);
 
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/Json/JsonLocalizationDictionaryBuilder.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/Json/JsonLocalizationDictionaryBuilder.cs
index 04ec79aaf6..e4b66148a5 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/Json/JsonLocalizationDictionaryBuilder.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/Json/JsonLocalizationDictionaryBuilder.cs
@@ -2,7 +2,6 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Text.Json;
-using JetBrains.Annotations;
 using Microsoft.Extensions.Localization;
 
 namespace Volo.Abp.Localization.Json;
@@ -13,8 +12,7 @@ public static class JsonLocalizationDictionaryBuilder
     ///     Builds an <see cref="JsonLocalizationDictionaryBuilder" /> from given file.
     /// </summary>
     /// <param name="filePath">Path of the file</param>
-    [CanBeNull]
-    public static ILocalizationDictionary BuildFromFile(string filePath)
+    public static ILocalizationDictionary? BuildFromFile(string filePath)
     {
         try
         {
@@ -38,10 +36,9 @@ public static class JsonLocalizationDictionaryBuilder
     ///     Builds an <see cref="JsonLocalizationDictionaryBuilder" /> from given json string.
     /// </summary>
     /// <param name="jsonString">Json string</param>
-    [CanBeNull]
-    public static ILocalizationDictionary BuildFromJsonString(string jsonString)
+    public static ILocalizationDictionary? BuildFromJsonString(string jsonString)
     {
-        JsonLocalizationFile jsonFile;
+        JsonLocalizationFile? jsonFile;
         try
         {
             jsonFile = JsonSerializer.Deserialize<JsonLocalizationFile>(jsonString, DeserializeOptions);
@@ -50,6 +47,11 @@ public static class JsonLocalizationDictionaryBuilder
         {
             throw new AbpException("Can not parse json string. " + ex.Message);
         }
+
+        if (jsonFile == null)
+        {
+            return null;
+        }
         
         var cultureCode = jsonFile.Culture;
         if (string.IsNullOrEmpty(cultureCode))
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/Json/JsonLocalizationFile.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/Json/JsonLocalizationFile.cs
index 08daf70682..8470e2696f 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/Json/JsonLocalizationFile.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/Json/JsonLocalizationFile.cs
@@ -7,7 +7,7 @@ public class JsonLocalizationFile
     /// <summary>
     /// Culture name; eg : en , en-us, zh-CN
     /// </summary>
-    public string Culture { get; set; }
+    public string Culture { get; set; } = default!;
 
     public Dictionary<string, string> Texts { get; set; }
 
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LanguageInfo.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LanguageInfo.cs
index 9183b89c4e..a2274b5a69 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LanguageInfo.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LanguageInfo.cs
@@ -8,19 +8,18 @@ namespace Volo.Abp.Localization;
 public class LanguageInfo : ILanguageInfo
 {
     [NotNull]
-    public virtual string CultureName { get; protected set; }
+    public virtual string CultureName { get; protected set; } = default!;
 
     [NotNull]
-    public virtual string UiCultureName { get; protected set; }
+    public virtual string UiCultureName { get; protected set; } = default!;
 
     [NotNull]
-    public virtual string DisplayName { get; protected set; }
+    public virtual string DisplayName { get; protected set; } = default!;
 
     [NotNull]
-    public virtual string TwoLetterISOLanguageName { get; protected set; }
+    public virtual string TwoLetterISOLanguageName { get; protected set; } = default!;
 
-    [CanBeNull]
-    public virtual string FlagIcon { get; set; }
+    public virtual string? FlagIcon { get; set; }
 
     
     protected LanguageInfo()
@@ -30,30 +29,30 @@ public class LanguageInfo : ILanguageInfo
 
     public LanguageInfo(
         string cultureName,
-        string uiCultureName = null,
-        string displayName = null,
-        string flagIcon = null)
+        string? uiCultureName = null,
+        string? displayName = null,
+        string? flagIcon = null)
     {
         ChangeCultureInternal(cultureName, uiCultureName, displayName);
         FlagIcon = flagIcon;
     }
 
-    public virtual void ChangeCulture(string cultureName, string uiCultureName = null, string displayName = null)
+    public virtual void ChangeCulture(string cultureName, string? uiCultureName = null, string? displayName = null)
     {
         ChangeCultureInternal(cultureName, uiCultureName, displayName);
     }
 
-    private void ChangeCultureInternal(string cultureName, string uiCultureName, string displayName)
+    private void ChangeCultureInternal(string cultureName, string? uiCultureName, string? displayName)
     {
         CultureName = Check.NotNullOrWhiteSpace(cultureName, nameof(cultureName));
 
-        UiCultureName = !uiCultureName.IsNullOrWhiteSpace()
+        UiCultureName = (!uiCultureName.IsNullOrWhiteSpace()
             ? uiCultureName
-            : cultureName;
+            : cultureName)!;
 
-        DisplayName = !displayName.IsNullOrWhiteSpace()
+        DisplayName = (!displayName.IsNullOrWhiteSpace()
             ? displayName
-            : cultureName;
+            : cultureName)!;
         
         TwoLetterISOLanguageName = new CultureInfo(cultureName)
             .TwoLetterISOLanguageName;
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LanguageInfoExtensions.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LanguageInfoExtensions.cs
index 8909708b67..7b60cce40d 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LanguageInfoExtensions.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LanguageInfoExtensions.cs
@@ -6,10 +6,10 @@ namespace Volo.Abp.Localization;
 
 public static class LanguageInfoExtensions
 {
-    public static T FindByCulture<T>(
+    public static T? FindByCulture<T>(
         [NotNull] this IEnumerable<T> languages,
         [NotNull] string cultureName,
-        [CanBeNull] string uiCultureName = null)
+        string? uiCultureName = null)
     where T : class, ILanguageInfo
     {
         if (uiCultureName == null)
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizableStringSerializer.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizableStringSerializer.cs
index 5006d62ea8..02b9cc8fac 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizableStringSerializer.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizableStringSerializer.cs
@@ -13,7 +13,7 @@ public class LocalizableStringSerializer : ILocalizableStringSerializer, ITransi
         LocalizationOptions = localizationOptions.Value;
     }
 
-    public virtual string Serialize(ILocalizableString localizableString)
+    public virtual string? Serialize(ILocalizableString? localizableString)
     {
         if (localizableString == null)
         {
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResource.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResource.cs
index 7a55f1f8a3..b6e0da82e4 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResource.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResource.cs
@@ -12,8 +12,8 @@ public class LocalizationResource : LocalizationResourceBase
 
     public LocalizationResource(
         [NotNull] Type resourceType,
-        [CanBeNull] string defaultCultureName = null,
-        [CanBeNull] ILocalizationResourceContributor initialContributor = null)
+        string? defaultCultureName = null,
+        ILocalizationResourceContributor? initialContributor = null)
         : base(
             LocalizationResourceNameAttribute.GetName(resourceType),
             defaultCultureName,
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceBase.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceBase.cs
index a7ec4fb93b..6cbbd98188 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceBase.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceBase.cs
@@ -10,16 +10,15 @@ public abstract class LocalizationResourceBase
     
     public List<string> BaseResourceNames { get; }
     
-    [CanBeNull]
-    public string DefaultCultureName { get; set; }
+    public string? DefaultCultureName { get; set; }
     
     [NotNull]
     public LocalizationResourceContributorList Contributors { get; }
 
     public LocalizationResourceBase(
         [NotNull] string resourceName,
-        [CanBeNull] string defaultCultureName = null,
-        [CanBeNull] ILocalizationResourceContributor initialContributor = null)
+        string? defaultCultureName = null,
+        ILocalizationResourceContributor? initialContributor = null)
     {
         ResourceName = Check.NotNullOrWhiteSpace(resourceName, nameof(resourceName));
         DefaultCultureName = defaultCultureName;
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceContributorList.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceContributorList.cs
index 6df15920da..9f11aa4051 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceContributorList.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceContributorList.cs
@@ -7,7 +7,7 @@ namespace Volo.Abp.Localization;
 
 public class LocalizationResourceContributorList : List<ILocalizationResourceContributor>
 {
-    public LocalizedString GetOrNull(
+    public LocalizedString? GetOrNull(
         string cultureName,
         string name,
         bool includeDynamicContributors = true)
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceDictionary.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceDictionary.cs
index 4a88eac199..f6487a85b7 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceDictionary.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/LocalizationResourceDictionary.cs
@@ -8,12 +8,12 @@ public class LocalizationResourceDictionary : Dictionary<string, LocalizationRes
 {
     private readonly Dictionary<Type, LocalizationResourceBase> _resourcesByTypes = new();
 
-    public LocalizationResource Add<TResouce>([CanBeNull] string defaultCultureName = null)
+    public LocalizationResource Add<TResouce>(string? defaultCultureName = null)
     {
         return Add(typeof(TResouce), defaultCultureName);
     }
 
-    public LocalizationResource Add(Type resourceType, [CanBeNull] string defaultCultureName = null)
+    public LocalizationResource Add(Type resourceType, string? defaultCultureName = null)
     {
         var resourceName = LocalizationResourceNameAttribute.GetName(resourceType);
         if (ContainsKey(resourceName))
@@ -29,7 +29,7 @@ public class LocalizationResourceDictionary : Dictionary<string, LocalizationRes
         return resource;
     }
     
-    public NonTypedLocalizationResource Add([NotNull] string resourceName, [CanBeNull] string defaultCultureName = null)
+    public NonTypedLocalizationResource Add([NotNull] string resourceName, string? defaultCultureName = null)
     {
         Check.NotNullOrWhiteSpace(resourceName, nameof(resourceName));
         
@@ -80,7 +80,7 @@ public class LocalizationResourceDictionary : Dictionary<string, LocalizationRes
         return resource;
     }
 
-    public LocalizationResourceBase GetOrNull(Type resourceType)
+    public LocalizationResourceBase? GetOrNull(Type resourceType)
     {
         return _resourcesByTypes.GetOrDefault(resourceType);
     }
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/NonTypedLocalizationResource.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/NonTypedLocalizationResource.cs
index 2a8300d522..6495eb8164 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/NonTypedLocalizationResource.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/NonTypedLocalizationResource.cs
@@ -6,8 +6,8 @@ public class NonTypedLocalizationResource : LocalizationResourceBase
 {
     public NonTypedLocalizationResource(
         [NotNull] string resourceName,
-        [CanBeNull] string defaultCultureName = null,
-        [CanBeNull] ILocalizationResourceContributor initialContributor = null
+        string? defaultCultureName = null,
+        ILocalizationResourceContributor? initialContributor = null
     ) : base(
         resourceName,
         defaultCultureName,
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/StaticLocalizationDictionary.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/StaticLocalizationDictionary.cs
index 17c08a11d2..b363076fe0 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/StaticLocalizationDictionary.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/StaticLocalizationDictionary.cs
@@ -25,7 +25,7 @@ public class StaticLocalizationDictionary : ILocalizationDictionary
     }
 
     /// <inheritdoc/>
-    public virtual LocalizedString GetOrNull(string name)
+    public virtual LocalizedString? GetOrNull(string name)
     {
         return Dictionary.GetOrDefault(name);
     }
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/VirtualFiles/Json/JsonVirtualFileLocalizationResourceContributor.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/VirtualFiles/Json/JsonVirtualFileLocalizationResourceContributor.cs
index fcafed49f3..71ca2744a0 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/VirtualFiles/Json/JsonVirtualFileLocalizationResourceContributor.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/VirtualFiles/Json/JsonVirtualFileLocalizationResourceContributor.cs
@@ -19,7 +19,7 @@ public class JsonVirtualFileLocalizationResourceContributor : VirtualFileLocaliz
         return file.Name.EndsWith(".json", StringComparison.OrdinalIgnoreCase);
     }
 
-    protected override ILocalizationDictionary CreateDictionaryFromFileContent(string jsonString)
+    protected override ILocalizationDictionary? CreateDictionaryFromFileContent(string jsonString)
     {
         return JsonLocalizationDictionaryBuilder.BuildFromJsonString(jsonString);
     }
diff --git a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/VirtualFiles/VirtualFileLocalizationResourceContributorBase.cs b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/VirtualFiles/VirtualFileLocalizationResourceContributorBase.cs
index 40bb9de7c5..d87169ea31 100644
--- a/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/VirtualFiles/VirtualFileLocalizationResourceContributorBase.cs
+++ b/framework/src/Volo.Abp.Localization/Volo/Abp/Localization/VirtualFiles/VirtualFileLocalizationResourceContributorBase.cs
@@ -16,11 +16,11 @@ public abstract class VirtualFileLocalizationResourceContributorBase : ILocaliza
     public bool IsDynamic => false;
 
     private readonly string _virtualPath;
-    private IVirtualFileProvider _virtualFileProvider;
-    private Dictionary<string, ILocalizationDictionary> _dictionaries;
+    private IVirtualFileProvider _virtualFileProvider = default!;
+    private Dictionary<string, ILocalizationDictionary>? _dictionaries;
     private bool _subscribedForChanges;
     private readonly object _syncObj = new object();
-    private LocalizationResourceBase _resource;
+    private LocalizationResourceBase _resource = default!;
 
     protected VirtualFileLocalizationResourceContributorBase(string virtualPath)
     {
@@ -33,7 +33,7 @@ public abstract class VirtualFileLocalizationResourceContributorBase : ILocaliza
         _virtualFileProvider = context.ServiceProvider.GetRequiredService<IVirtualFileProvider>();
     }
 
-    public virtual LocalizedString GetOrNull(string cultureName, string name)
+    public virtual LocalizedString? GetOrNull(string cultureName, string name)
     {
         return GetDictionaries().GetOrDefault(cultureName)?.GetOrNull(name);
     }
@@ -118,8 +118,7 @@ public abstract class VirtualFileLocalizationResourceContributorBase : ILocaliza
 
     protected abstract bool CanParseFile(IFileInfo file);
 
-    [CanBeNull]
-    protected virtual ILocalizationDictionary CreateDictionaryFromFile(IFileInfo file)
+    protected virtual ILocalizationDictionary? CreateDictionaryFromFile(IFileInfo file)
     {
         using (var stream = file.CreateReadStream())
         {
@@ -127,6 +126,5 @@ public abstract class VirtualFileLocalizationResourceContributorBase : ILocaliza
         }
     }
 
-    [CanBeNull] 
-    protected abstract ILocalizationDictionary CreateDictionaryFromFileContent(string fileContent);
+    protected abstract ILocalizationDictionary? CreateDictionaryFromFileContent(string fileContent);
 }