def nud(self, context):
raise InvalidTokenError(<EOL>"<STR_LIT>" % (<EOL>self, context.current_pos))<EOL>
Null denotation.

        Describes what happens to this token when located at the beginning of
        an expression.

        Args:
            context (Parser): the parser from which next tokens/subexpressions
                can be retrieved

        Returns:
            object: Parsed value for this token (a node, a value, ...)