Clears the score.

        raise:  NoAccess - ``Metadata.isRequired()`` or
                ``Metadata.isReadOnly()`` is ``true``
        *compliance: mandatory -- This method must be implemented.*

def clear_score(self):
        """Clears the score.

        raise:  NoAccess - ``Metadata.isRequired()`` or
                ``Metadata.isReadOnly()`` is ``true``
        *compliance: mandatory -- This method must be implemented.*

        """
        if self._grade_system.is_based_on_grades():
            return  # do nothing, spec does not raise error
        if (self.get_score_metadata().is_read_only() or
                self.get_score_metadata().is_required()):
            raise errors.NoAccess()
        self._my_map['score'] = self._score_default
        self._my_map['gradingAgentId'] = ''
        self._my_map['timeGraded'] = None