code: def get_grade_id(self):
          
          # Implemented from template for osid.learning.Activity.get_objective_id
          if not bool(self._my_map['gradeId']):
              raise errors.IllegalState('grade empty')
          return Id(self._my_map['gradeId'])
docs: Gets the grade ``Id`` in this entry if the grading system is based on grades.
  
          return: (osid.id.Id) - the grade ``Id``
          raise:  IllegalState - ``is_graded()`` is ``false`` or
                  ``GradeSystem.isBasedOnGrades()`` is ``false``
          *compliance: mandatory -- This method must be implemented.*