fix: assign empty list and append it later currently not supported

Refs: OO-LD/oold-python#3

Author: simontaurus

src/osw/ontology.py

@@ -810,9 +810,7 @@ def _store_ontology(self, param: StoreOntologyParam):
             if namespace == "Category":
                 smw_import_type = "Category"
                 if not hasattr(e, "subclass_of") or e.subclass_of is None:
-                    e.subclass_of = []
-                if len(e.subclass_of) == 0:
-                    e.subclass_of.append(self.import_config.meta_class_title)
+                    e.subclass_of = [self.import_config.meta_class_title]
             elif namespace == "Property":
                 smw_import_type = "Type:" + e.cast(model.Property).property_type
             else: