docs: def delete_question(self, question_id):
          """Deletes the ``Question`` identified by the given ``Id``.
  
          arg:    question_id (osid.id.Id): the ``Id`` of the ``Question``
                  to delete
          raise:  NotFound - a ``Question`` was not found identified by
                  the given ``Id``
          raise:  NullArgument - ``question_id`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure occurred
          *compliance: mandatory -- This method must be implemented.*
  
          """
          collection = JSONClientValidated('assessment',
                                           collection='Item',
                                           runtime=self._runtime)
          if not isinstance(question_id, ABCId):
              raise errors.InvalidArgument('the argument is not a valid OSID Id')
          item = collection.find_one({'question._id': ObjectId(question_id.get_identifier())})
  
          item['question'] = None
          collection.save(item)