Fix possible `null` errors.

Resolve #17766

modules/identity/src/Volo.Abp.Identity.EntityFrameworkCore/Volo/Abp/Identity/EntityFrameworkCore/EfCoreOrganizationUnitRepository.cs

@@ -40,7 +40,7 @@ public class EfCoreOrganizationUnitRepository
     {
         return await (await GetDbSetAsync())
             .IncludeDetails(includeDetails)
-            .Where(ou => ou.Code.StartsWith(code) && ou.Id != parentId.Value)
+            .Where(ou => ou.Code.StartsWith(code) && ou.Id != parentId)
             .ToListAsync(GetCancellationToken(cancellationToken));
     }
 

modules/identity/src/Volo.Abp.Identity.MongoDB/Volo/Abp/Identity/MongoDB/MongoOrganizationUnitRepository.cs

@@ -39,7 +39,7 @@ public class MongoOrganizationUnitRepository
         CancellationToken cancellationToken = default)
     {
         return await (await GetMongoQueryableAsync(cancellationToken))
-                .Where(ou => ou.Code.StartsWith(code) && ou.Id != parentId.Value)
+                .Where(ou => ou.Code.StartsWith(code) && ou.Id != parentId)
                 .ToListAsync(GetCancellationToken(cancellationToken));
     }
 

modules/identity/test/Volo.Abp.Identity.TestBase/Volo/Abp/Identity/OrganizationUnitRepository_Tests.cs

@@ -47,8 +47,13 @@ public abstract class OrganizationUnitRepository_Tests<TStartupModule> : AbpIden
     [Fact]
     public async Task GetAllChildrenWithParentCodeAsync()
     {
-        (await _organizationUnitRepository.GetAllChildrenWithParentCodeAsync(OrganizationUnit.CreateCode(0),
-            _guidGenerator.Create())).ShouldNotBeNull();
+        var allChildren = await _organizationUnitRepository.GetAllChildrenWithParentCodeAsync(OrganizationUnit.CreateCode(0), _guidGenerator.Create());
+        allChildren.ShouldNotBeNull();
+        allChildren.ShouldBeEmpty();
+
+        allChildren = (await _organizationUnitRepository.GetAllChildrenWithParentCodeAsync(OrganizationUnit.CreateCode(1), null));
+        allChildren.ShouldNotBeNull();
+        allChildren.ShouldNotBeEmpty();
     }
 
     [Fact]