docs: def validate(self, value, model=None, context=None):
          """
          Validate
          Perform value validation and return result
  
          :param value:           value to check
          :param model:           parent model being validated
          :param context:         object or None, validation context
          :return:                shiftschema.results.Error
          """
  
          if not isinstance(value, Iterable):
              return Error(self.not_iterable)
  
          try:
              next(iter(value))
          except StopIteration:
              return Error(self.cant_be_empty)
  
          return Error()