title: StrongLoop loopback - how to exclude results without related model results
body: <p>I'm using this Node API JSON, which returns Customers, their instances, and the instance versions. </p>
  
  <pre><code>Customers.find({
      "include": {
          "relation": "instances",
          "scope": {
              "include": {
                  "relation": "versions"
              }
          }
      }
  });
  </code></pre>
  
  <p>I would like to exclude all customers which do not have any related instances, in the result JSON, there is an "instances" entry with empty [ ]. however when I try to use this in a "where" I get a server error... any ideas, or am I going about this the wrong way? </p>