fix: treat None cursors as a no-op. (#440)

start_at(None) was causing an error. Address that and treat this as a no-op

Author: crwilcox

google/cloud/firestore_v1/base_query.py

@@ -755,7 +755,7 @@ def _normalize_cursor(self, cursor, orders) -> Optional[Tuple[Any, Any]]:
 
  document_fields = values
 
- if len(document_fields) > len(orders):
+ if document_fields and len(document_fields) > len(orders):
  msg = _MISMATCH_CURSOR_W_ORDER_BY.format(document_fields, order_keys)
  raise ValueError(msg)
 

tests/unit/v1/test_base_query.py

@@ -726,6 +726,14 @@ def test__normalize_orders_wo_orders_w_snapshot_cursor_w_neq_where(self):
  ]
  self.assertEqual(query._normalize_orders(), expected)
 
+ def test__normalize_orders_w_name_orders_w_none_cursor(self):
+ collection = self._make_collection("here")
+ query = (
+ self._make_one(collection).order_by("__name__", "DESCENDING").start_at(None)
+ )
+ expected = [query._make_order("__name__", "DESCENDING")]
+ self.assertEqual(query._normalize_orders(), expected)
+
  def test__normalize_cursor_none(self):
  query = self._make_one(mock.sentinel.parent)
  self.assertIsNone(query._normalize_cursor(None, query._orders))