revert: Revert work item None removal

capella2polarion/converters/element_converter.py

@@ -120,13 +120,8 @@ def __init__(
 
     def serialize_all(self) -> list[data_models.CapellaWorkItem]:
         """Serialize all items of the converter_session."""
-        work_items = {
-            uuid: self.serialize(uuid) for uuid in self.converter_session
-        }
-        for uuid, work_item in work_items.items():
-            if work_item is None:
-                del self.converter_session[uuid]
-        return list(filter(None, work_items.values()))
+        work_items = [self.serialize(uuid) for uuid in self.converter_session]
+        return list(filter(None, work_items))
 
     def serialize(self, uuid: str) -> data_models.CapellaWorkItem | None:
         """Return a CapellaWorkItem for the given diagram or element."""