code: def resolve_field_instance(cls_or_instance):
      
      if isinstance(cls_or_instance, type):
          if not issubclass(cls_or_instance, FieldABC):
              raise FieldInstanceResolutionError
          return cls_or_instance()
      else:
          if not isinstance(cls_or_instance, FieldABC):
              raise FieldInstanceResolutionError
          return cls_or_instance
docs: Return a Schema instance from a Schema class or instance.
  
      :param type|Schema cls_or_instance: Marshmallow Schema class or instance.