docs: def get_numeric_score_increment(self):
          """Gets the incremental step.
  
          return: (decimal) - the increment
          raise:  IllegalState - ``is_based_on_grades()`` is ``true``
          *compliance: mandatory -- This method must be implemented.*
  
          """
          if self.is_based_on_grades():
              raise errors.IllegalState('This GradeSystem is based on grades')
          if self._my_map['numericScoreIncrement'] is None:
              return None
          else:
              return Decimal(str(self._my_map['numericScoreIncrement']))