docs: def update_gradebook_column(self, gradebook_column_form):
          """Updates an existing gradebook column.
  
          arg:    gradebook_column_form
                  (osid.grading.GradebookColumnForm): the form containing
                  the elements to be updated
          raise:  IllegalState - ``gradebook_column_form`` already used in
                  an update transaction
          raise:  InvalidArgument - the form contains an invalid value
          raise:  NullArgument - ``gradebook_column_form`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          raise:  Unsupported - ``gradebook_column_form`` did not
                  originate from
                  ``get_gradebook_column_form_for_update()``
          *compliance: mandatory -- This method must be implemented.*
  
          """
          collection = JSONClientValidated('grading',
                                           collection='GradebookColumn',
                                           runtime=self._runtime)
          if not isinstance(gradebook_column_form, ABCGradebookColumnForm):
              raise errors.InvalidArgument('argument type is not an GradebookColumnForm')
          if not gradebook_column_form.is_for_update():
              raise errors.InvalidArgument('the GradebookColumnForm is for update only, not create')
          try:
              if self._forms[gradebook_column_form.get_id().get_identifier()] == UPDATED:
                  raise errors.IllegalState('gradebook_column_form already used in an update transaction')
          except KeyError:
              raise errors.Unsupported('gradebook_column_form did not originate from this session')
          if not gradebook_column_form.is_valid():
              raise errors.InvalidArgument('one or more of the form elements is invalid')
  
          # check that there are no entries, if updating the gradeSystemId
          old_column = collection.find_one({"_id": gradebook_column_form._my_map['_id']})
          if old_column['gradeSystemId'] != gradebook_column_form._my_map['gradeSystemId']:
              if self._has_entries(gradebook_column_form.id_):
                  raise errors.IllegalState('Entries exist in this gradebook column. ' +
                                            'Cannot change the grade system.')
  
          collection.save(gradebook_column_form._my_map)
  
          self._forms[gradebook_column_form.get_id().get_identifier()] = UPDATED
  
          # Note: this is out of spec. The OSIDs don't require an object to be returned:
          return objects.GradebookColumn(
              osid_object_map=gradebook_column_form._my_map,
              runtime=self._runtime,
              proxy=self._proxy)