code: def ValidateRequiredFieldsAreNotEmpty(gtfs_object, required_field_names,
                                        problems=None):
    
    no_missing_value = True
    for name in required_field_names:
      if IsEmpty(getattr(gtfs_object, name, None)):
        if problems:
          problems.MissingValue(name)
        no_missing_value = False
    return no_missing_value
docs: Validates whether all required fields of an object have a value:
      - if value empty adds MissingValue errors (if problems accumulator is
        provided)