Readme instructions: error with PG: "Cannot return null for non-nullable field User.id."

[frederikhors]

REPRODUCTION HERE: https://glitch.com/edit/#!/postgres-join-monster-1

It seems something is broken in your Readme instructions.

I reproduced it and it gives to me an error: "Cannot return null for non-nullable field User.id."

Query:

query {
  user(id: 1) {
    id
    fullName
    email
    posts {
      id
      body
      numComments
      comments {
        id
        body
        userId
      }
    }
  }
}