fix test_default_index_warning_not_raised_by_read_gbq_primary_key

Author: chelsea-lin

bigframes/session/_io/bigquery/read_gbq_table.py

@@ -250,6 +250,10 @@ def get_index_cols(
  column(s), then return those too so that ordering generation can be
  avoided.
  """
+ # Transform index_col -> index_cols so we have a variable that is
+ # always a list of column names (possibly empty).
+ schema_len = len(table.schema)
+
  index_cols: List[str] = []
  if isinstance(index_col, bigframes.enums.DefaultIndexKind):
  if index_col == bigframes.enums.DefaultIndexKind.SEQUENTIAL_INT64:
@@ -265,14 +269,7 @@ def get_index_cols(
  raise NotImplementedError(
  f"Got unexpected index_col {repr(index_col)}. {constants.FEEDBACK_LINK}"
  )
- elif isinstance(index_col, Iterable) and len(list(index_col)) == 0:
- return []
-
- # Transform index_col -> index_cols so we have a variable that is
- # always a list of column names (possibly empty).
- schema_len = len(table.schema)
-
- if isinstance(index_col, str):
+ elif isinstance(index_col, str):
  if rename_to_schema is not None:
  index_col = rename_to_schema.get(index_col, index_col)
  index_cols = [index_col]