title: RethinkDB: RqlRuntimeError: Cannot perform bracket on a sequence of sequences
body: <p>Given the following documents in a table:</p>
  
  <pre><code>[
    {
      "id": "d30aa369-99d6-4a40-9547-2cbdf0bb069a",
      "locations": [
        {
          "alerts": [
            {"person": 200},
            {"person": 300}
          ],
          "name": "home"
        },
        {
          "alerts": [
            {"person": 200},
            {"person": 300}
          ],
          "name": "work"
        }
      ],
      "person": 100
    },
    {
      "id": "d671d2c7-0e0d-43c0-9148-9e6b049b49a7",
      "locations": [
        {
          "alerts": [
            {"person": 100},
            {"person": 300}
          ],
          "name": "home"
        },
        {
          "alerts": [
            {"person": 100},
            {"person": 300}
          ],
          "name": "work"
        }
      ],
      "person": 200
    }
  ] 
  </code></pre>
  
  <p>I want to return all locations that have an alert containing a particular person. I thought it would go a little something like this:</p>
  
  <pre><code>r.db('db').table('test')('locations').filter(function(location){
    return location('alerts')('person').eq(200);
  });
  </code></pre>
  
  <p>Yet I get:</p>
  
  <blockquote>
    <p>RqlRuntimeError: Cannot perform bracket on a sequence of sequences in:</p>
  </blockquote>
  
  <p>What is the correct way to execute this query?</p>