wtforms FieldList 报错，求解？

class OptionForm(Form):
    order_num= IntegerField(validators=[DataRequired()])
    opt_cont=StringField(validators=[DataRequired()])


class QuestionForm(Form):
    genre=IntegerField(validators=[DataRequired()])
    questiontext=StringField(validators=[DataRequired()])
    answer=StringField(validators=[DataRequired()])
    paper_id=IntegerField(validators=[DataRequired()])

    option=FieldList(FormField(OptionForm))

错误提示：TypeError: init() got an unexpected keyword argument 'formdata'
option=FieldList(StringField())
就不会报错，还能拿到值。

{
  "answer": "1",
  "genre": 1,
  "option": [
    {
      "opt_cont": "我是一个选项",
      "order_num": 1
    }
  ],
  "paper_id": 1,
  "questiontext": "今天吃什么？"
}

type(option)=list
type(option[0])=dict