def validate_types(self, types=None):
types = types or self.default_types<EOL>if types is None:<EOL><INDENT>types = []<EOL><DEDENT>if isinstance(types, six.string_types):<EOL><INDENT>types = [types]<EOL><DEDENT>return types<EOL>
Return a valid list of types.

        `types` may be a string or a list of strings.
        If `types` is not supplied, returns the default_types.