diff --git a/polarion_rest_api_client/open_api_client/models/errors_errors_item.py b/polarion_rest_api_client/open_api_client/models/errors_errors_item.py
index 97020bb7..f90a1b5c 100644
--- a/polarion_rest_api_client/open_api_client/models/errors_errors_item.py
+++ b/polarion_rest_api_client/open_api_client/models/errors_errors_item.py
@@ -72,7 +72,7 @@ def from_dict(cls: Type[T], src_dict: Dict[str, Any]) -> T:
 
         _source = d.pop("source", UNSET)
         source: Union[Unset, ErrorsErrorsItemSource]
-        if isinstance(_source, Unset):
+        if isinstance(_source, (Unset, type(None))):
             source = UNSET
         else:
             source = ErrorsErrorsItemSource.from_dict(_source)
diff --git a/polarion_rest_api_client/open_api_client/models/errors_errors_item_source.py b/polarion_rest_api_client/open_api_client/models/errors_errors_item_source.py
index c91c7815..3151b2e8 100644
--- a/polarion_rest_api_client/open_api_client/models/errors_errors_item_source.py
+++ b/polarion_rest_api_client/open_api_client/models/errors_errors_item_source.py
@@ -67,7 +67,7 @@ def from_dict(cls: Type[T], src_dict: Dict[str, Any]) -> T:
 
         _resource = d.pop("resource", UNSET)
         resource: Union[Unset, ErrorsErrorsItemSourceResource]
-        if isinstance(_resource, Unset):
+        if isinstance(_resource, (Unset, type(None))):
             resource = UNSET
         else:
             resource = ErrorsErrorsItemSourceResource.from_dict(_resource)