message: Update RemapOperatorType with ValueError
diff: @@ -236,6 +236,8 @@ class Converter(object):
  operator_type: String representing the builtin operator data type
  string.
  (see :schema.fbs).
  + Raises:
  + ValueError: When the model has consistency problems.
  Returns:
  Upgraded builtin operator data type as a string.
  """
  