title: Graphql query only not null objects
body: <p>im trying to perform a query like this:</p>
  
  <pre><code>{
   people{
     pet{
       name
     }
   }
  }
  </code></pre>
  
  <p>result:</p>
  
  <pre><code>{
   "people": {
     "pet": null
   }
  },
  {
   "people": {
     "pet": {
       name: "steve"
    }
   }
  }
  </code></pre>
  
  <p>What i want is to get only people that contains a pet, is there any way to achieve this not coding on my resolver ?</p>