tests: add column_metadata=None variant for METADATA_CHANGED warning path

The existing test used column_metadata=[] (falsy empty list).  The warning
branch also triggers for None (attribute absent entirely), which has different
semantics — it indicates the field was never set rather than explicitly empty.

The new test ensures both falsy forms trigger the warning and update
result_metadata_id without touching result_metadata.

Author: nikagra

tests/unit/test_response_future.py

@@ -1214,9 +1214,41 @@ def test_set_result_warns_when_metadata_id_but_no_column_metadata(self):
         # metadata_id is still updated even without column metadata
         assert ps.result_metadata_id == b'new_id'
 
-    # -------------------------------------------------------------------------
-    # _query: per-connection feature gating for skip_meta / result_metadata_id
-    # -------------------------------------------------------------------------
+    def test_set_result_warns_when_metadata_id_but_column_metadata_is_none(self):
+        """
+        Like the empty-list variant above, but column_metadata=None (attribute
+        absent rather than explicitly empty).  Both None and [] are falsy, so
+        the warning branch should be taken and result_metadata_id updated.
+        """
+        session = self.make_session()
+        pool = session._pools.get.return_value
+        connection = Mock(spec=Connection)
+        connection.protocol_version = 4
+        connection.features = Mock()
+        connection.features.use_metadata_id = False
+        pool.borrow_connection.return_value = (connection, 1)
+
+        ps = Mock()
+        ps.result_metadata = [('ks', 'tb', 'col', Mock())]
+        ps.result_metadata_id = b'old_id'
+
+        rf = self.make_response_future(session)
+        rf.prepared_statement = ps
+        rf.send_request()
+
+        response = self._make_rows_response(
+            result_metadata_id=b'new_id',
+            column_metadata=None,
+        )
+
+        with self.assertLogs('cassandra.cluster', level='WARNING') as log_ctx:
+            rf._set_result(None, None, None, response)
+
+        assert any('result_metadata_id' in msg for msg in log_ctx.output)
+        # result_metadata_id is still updated; result_metadata must not be touched
+        assert ps.result_metadata_id == b'new_id'
+
+
 
     def test_query_sets_skip_meta_with_scylla_extension(self):
         """