def METHOD_NAME(self, lookup_name):
    if lookup_name == 'contains':
        return make_multistring_contains_lookup(self.delimiter)
    elif lookup_name == 'icontains':
        return make_multistring_icontains_lookup(self.delimiter)
    elif lookup_name == 'isnull':
        return builtin_lookups.IsNull
    raise NotImplementedError(
        "Lookup '{}' doesn't work with MultiStringField".format(lookup_name),
    )