title: GraphQL fallback query if no results
body: <p>I have the following query:</p>
  
  <pre><code>{
       entity(id: "theId") {
           source1: media(source: 1){
               images{
                   src, alt
               }
           }
           source2: media(source: 2){
               images{
                   src, alt
               }
           }
       }
  }
  </code></pre>
  
  <p>That give me a result like:</p>
  
  <pre><code>{
      "entity": [
        {
          "source1": {
              "images": [{"src": "", "alt": ""}]
          },
          "source2": {
              "images": [{"src": "", "alt": ""}]
          }
        }
      ]
  }
  </code></pre>
  
  <p>Is there a way to have a single result of <code>source1</code> and <code>source2</code>, executing <code>source1</code> and if it has no result it use <code>source2</code> as fallback?</p>