Graphql Gatsby CreateResolver与runQuery返回错误

下面是Gatsby文档中的示例，但在尝试使用模式的explorer视图时出错：

exports.createResolvers = ({ createResolvers }) => {
  const resolvers = {
    Product: {
      categorySlug: {
        type: ["Category"],
        resolve(source, args, context, info) {
          return context.nodeModel.runQuery({
            query: { 
              filter: { 
                name: { eq: source.category } 
              } 
            },
            type: "Category",
            firstOnly: true,
          })
        },
      },
    },
  }

  createResolvers(resolvers)
}

资源管理器中的错误：

"message": "Field \"categorySlug\" of type \"[Category]\" must have a selection of subfields. Did you mean \"categorySlug { ... }\"?",