code: def clear_score(self):
          
          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
docs: Clears the score.
  
          raise:  NoAccess - ``Metadata.isRequired()`` or
                  ``Metadata.isReadOnly()`` is ``true``
          *compliance: mandatory -- This method must be implemented.*