code: def _varargs_labels_as_list(label_list):
      
      if len(label_list) == 0:
          return []
      elif not _is_non_string_iterable(label_list[0]):
          # Assume everything is a label.  If not, it'll be caught later.
          return label_list
      elif len(label_list) == 1:
          return label_list[0]
      else:
          raise ValueError("Labels {} contain more than list.".format(label_list),
                           "Pass just one list of labels.")
docs: Return a list of labels for a list of labels or singleton list of list
      of labels.