code: def create_field(self, work_item_field, project=None):
          
          route_values = {}
          if project is not None:
              route_values['project'] = self._serialize.url('project', project, 'str')
          content = self._serialize.body(work_item_field, 'WorkItemField')
          response = self._send(http_method='POST',
                                location_id='b51fd764-e5c2-4b9b-aaf7-3395cf4bdd94',
                                version='5.1-preview.2',
                                route_values=route_values,
                                content=content)
          return self._deserialize('WorkItemField', response)
docs: CreateField.
          [Preview API] Create a new field.
          :param :class:`<WorkItemField> <azure.devops.v5_1.work_item_tracking.models.WorkItemField>` work_item_field: New field definition
          :param str project: Project ID or project name
          :rtype: :class:`<WorkItemField> <azure.devops.v5_1.work-item-tracking.models.WorkItemField>`