title: query malformed, no start_object after query name
body: <p>I am running this query against AWS Elasticsearch 5.1 and getting a malformed query error. Here is the body of the request. I am basically just checking if the field exists during the time range.</p>
  
  <pre><code>{
    "query": {
      "bool": {
        "filter": {
          "bool": {
            "must": [
              {
                "range": {
                  "@timestamp": {
                    "gt": "2017-03-21T15:37:08.595919Z",
                    "lte": "2017-04-21T15:52:08.595919Z"
                  }
                }
              },
              {
                "query": [
                  {
                    "query_string": {
                      "query": "_exists_: $event.supplier"
                    }
                  }
                ]
              }
            ]
          }
        }
      }
    },
    "sort": [
      {
        "@timestamp": {
          "order": "asc"
        }
      }
    ]
  }
  </code></pre>