Set the _ef_search field to None by default in pgvector

Author: michaelbautin

ann_benchmarks/algorithms/pgvector/module.py

@@ -82,6 +82,7 @@ def __init__(self, psycopg_connect_kwargs: Dict[str, str]) -> None:
         self.prev_tuples_done = None
         self.prev_report_time_sec = None
         self.time_to_load_all_tuples_sec = None
+        self._ef_search = None
 
     def report_progress(
             self,