title: GraphQL nested query returning null field
body: <p>I'm trying to learn GraphQL (&amp; node.js &amp; MongoDB etc.). I cant get this simple nested query to return results :</p>
  
  <pre><code>query getLocationByPerson {
     People {
          firstName
          lastName
          service {
          location
        }
     }
  }
  </code></pre>
  
  <p>I only get the first level fields, like:</p>
  
  <pre><code>{
    "data": {
      "People": [
        {
          "firstName": "xxx",
          "lastName": "XXXXX",
          "service": null
        }
  }
  </code></pre>
  
  <p>Here's my schema:</p>
  
  <pre><code>type Query {
    People: [PeopleObject]!
    PeopleByName(lastName: String!): [PeopleObject]
    PeopleByID(id:ID!): [PeopleObject]
    Service: [ServiceObject]
    ServiceByID(id:ID!): [ServiceObject]
  }
  type PeopleObject {
      id: ID!
      Xid: String!
      firstName: String!
      lastName: String!
      email: String!
      serviceId: String
      apps: [String]
      service: [ServiceObject]
  }
  type ServiceObject {
      id: ID!
      name: String!
      location: String!
  }
  </code></pre>
  
  <p>And my resolver:</p>
  
  <pre><code>const queries = {
      People: () =&gt; People.find({}),
      PeopleByName: (root,args,context,info) =&gt; People.find({lastName: args.lastName}),
      PeopleByID: (root,args,context,info) =&gt; People.find({_id: args.id}),
      Service: () =&gt; Service.find({}),
      ServiceByID: (root,args,context,info) =&gt; Service.find({_id: args.id})
    };
  </code></pre>
  
  <p>Any idea what am I doing wrong?</p>