错误：与数据源关联的解析程序

Question

我从serverless.yml配置文件构建时遇到无服务器错误：Resolver associated with data sources：

# serverless.yml
...
mappingTemplates:
  - dataSource: Wallet
    type: Query
    field: walletFromId
    request: "_dynamo-get-wallet.txt"
    response: "_generic-result-response.txt"
  - dataSource: Wallet
    type: Query
    field: walletsFromUser
    request: "_dynamo-get-wallets-from-user.txt"
    response: "_generic-result-response.txt"
  - dataSource: Wallet
    type: Mutation
    field: registerWallet
    request: "_dynamo-put-wallet.txt"
    response: "_generic-result-response.txt"
dataSources:
  - type: AMAZON_DYNAMODB
    name: Wallet
    description: 'Wallet DataSource'
    config:
      tableName: "${self:custom.stage}-Wallet"
      serviceRoleArn: "arn:aws:iam::${self:custom.accountId}:role/${self:custom.appSync.serviceRole}"
...

我还有一个schema.graphql：

type Query {
    # query the wallet with given id and get the output with detail info
    walletFromId(walletId: String!): Wallet!
    # query wallets with given user id and get list of cards
    walletsFromUser(userId: String!): [Wallet!]!
}

type Mutation {
    # Add a wallet to an existing user
    registerWallet(userId: String!, number: String!, cvx: String!, expirationDate: String!): Wallet!
}
type Wallet {
    walletId: String!
    userId: String!
    number: String!
    cvx: String!
    expirationDate: String!
}

type Subscription {
    addWallet: Wallet
    @aws_subscribe(mutations: ["registerWallet"])
}

schema {
    query: Query
    mutation: Mutation
    subscription: Subscription
}

我找不到一个关于这个错误意味着什么的线索，而且我从构建日志中找不到任何其他东西。