PM-27248 [Defect] An unhandled error is returned when a MSP tries to import data (#6563)

* Revert previous commits and implement logic to avoid null references:

• reverted previous commits and force pushed to remove inconsistent formatting
• implemented logic to avoid null reference access (with comments)

* fix typo in comment

* fix logical error and add test coverage

* extracted logic common to all code paths per review comment

test/Core.Test/Tools/ImportFeatures/ImportCiphersAsyncCommandTests.cs

@@ -238,4 +238,55 @@ public class ImportCiphersAsyncCommandTests
         Assert.Equal("This organization can only have a maximum of " +
         $"{organization.MaxCollections} collections.", exception.Message);
     }
+
+    [Theory, BitAutoData]
+    public async Task ImportIntoOrganizationalVaultAsync_WithNullImportingOrgUser_SkipsCollectionUserCreation(
+        Organization organization,
+        Guid importingUserId,
+        List<Collection> collections,
+        List<CipherDetails> ciphers,
+        SutProvider<ImportCiphersCommand> sutProvider)
+    {
+        organization.MaxCollections = null;
+
+        foreach (var collection in collections)
+        {
+            collection.OrganizationId = organization.Id;
+        }
+
+        foreach (var cipher in ciphers)
+        {
+            cipher.OrganizationId = organization.Id;
+        }
+
+        KeyValuePair<int, int>[] collectionRelationships = {
+            new(0, 0),
+            new(1, 1),
+            new(2, 2)
+        };
+
+        sutProvider.GetDependency<IOrganizationRepository>()
+            .GetByIdAsync(organization.Id)
+            .Returns(organization);
+
+        // Simulate provider-created org with no members - importing user is NOT an org member
+        sutProvider.GetDependency<IOrganizationUserRepository>()
+            .GetByOrganizationAsync(organization.Id, importingUserId)
+            .Returns((OrganizationUser)null);
+
+        sutProvider.GetDependency<ICollectionRepository>()
+            .GetManyByOrganizationIdAsync(organization.Id)
+            .Returns(new List<Collection>());
+
+        await sutProvider.Sut.ImportIntoOrganizationalVaultAsync(collections, ciphers, collectionRelationships, importingUserId);
+
+        // Verify ciphers were created but no CollectionUser entries were created (because the organization user (importingUserId) is null)
+        await sutProvider.GetDependency<ICipherRepository>().Received(1).CreateAsync(
+            ciphers,
+            Arg.Is<IEnumerable<Collection>>(cols => cols.Count() == collections.Count),
+            Arg.Is<IEnumerable<CollectionCipher>>(cc => cc.Count() == ciphers.Count),
+            Arg.Is<IEnumerable<CollectionUser>>(cus => !cus.Any()));
+
+        await sutProvider.GetDependency<IPushNotificationService>().Received(1).PushSyncVaultAsync(importingUserId);
+    }
 }