RDBC-809 Method get_compare_exchange_values can't require object_type, set as optional

Author: poissoncorp

ravendb/documents/session/document_session.py

@@ -725,7 +725,7 @@ def lazily(self) -> LazySessionOperations:
             return self._session._lazily
 
         def graph_query(self, object_type: type, query: str):  # -> GraphDocumentQuery:
-            pass
+            raise NotImplementedError("Dropped support for graph queries")
 
         def what_changed(self) -> Dict[str, List[DocumentsChanges]]:
             return self._session._what_changed()