我是graphql.js的新手，我正在尝试构建一个嵌套的graphql类型。
目前我有一个GameStatistic类型，我想有一个Statistic类型有两个字段与GameStatistic类型。

const gameStatisticType = new GraphQLObjectType({
  name: 'GameStatistic',
  fields: {
    id: { type: GraphQLString },
    wagered: { type: GraphQLFloat },
    profit: { type: GraphQLFloat },
  },
});

exports.Type = new GraphQLObjectType({
  name: 'Statistic',
  fields: {
    dice: new GraphQLObjectType(gameStatisticType),
    wheel: new GraphQLObjectType(gameStatisticType),
  },
});

但它一直给出"The type of Statistic.wheel must be Output Type but got: undefined."和"The type of Statistic.dice must be Output Type but got: undefined."的误差
我到底做错了什么？