fix protocol

Author: Lingling Peng

synapseclient/models/curation.py

@@ -1584,7 +1584,7 @@ def list(
     def import_csv(
         self,
         file_handle_id: str,
-        csv_table_descriptor: Optional[CsvTableDescriptor] = None,
+        csv_table_descriptor: Optional[CsvTableDescriptor] = CsvTableDescriptor(),
         *,
         timeout: int = 120,
         synapse_client: Optional[Synapse] = None,