Return the function who has the least address that is greater than or equal to `addr`.

        :param int addr: The address to query.
        :return:         A Function instance, or None if there is no other function after `addr`.
        :rtype:          Function or None

def ceiling_func(self, addr):
        """
        Return the function who has the least address that is greater than or equal to `addr`.

        :param int addr: The address to query.
        :return:         A Function instance, or None if there is no other function after `addr`.
        :rtype:          Function or None
        """

        try:
            next_addr = self._function_map.ceiling_addr(addr)
            return self._function_map.get(next_addr)

        except KeyError:
            return None