code: def _fix_set_options(cls, options):
          
          optional_set_options = ('ignore', 'select')
          mandatory_set_options = ('add_ignore', 'add_select')
  
          def _get_set(value_str):
              """Split `value_str` by the delimiter `,` and return a set.
  
              Removes any occurrences of '' in the set.
              Also expand error code prefixes, to avoid doing this for every
              file.
  
              """
              return cls._expand_error_codes(set(value_str.split(',')) - {''})
  
          for opt in optional_set_options:
              value = getattr(options, opt)
              if value is not None:
                  setattr(options, opt, _get_set(value))
  
          for opt in mandatory_set_options:
              value = getattr(options, opt)
              if value is None:
                  value = ''
  
              if not isinstance(value, Set):
                  value = _get_set(value)
  
              setattr(options, opt, value)
  
          return options
docs: Alter the set options from None/strings to sets in place.