title: Nest MultiMatchQuery doesn't return result
body: <p>I'm trying to make a query which finds a presence of the word in different fields of the object <code>MyType</code> (all 11 fields <code>int</code> and <code>string</code>). In <em>Postman</em> the query below gives a result. </p>
  
  <p>Query by <em>Postman</em>:</p>
  
  <pre><code>http://esserver.com/_search
  {
     "query": {
        "multi_match" : {
           "query":    "word", 
           "fields": [ "field1", "field2", "field3", "field4", "field5", "field6", 
              "field7", "field8", "field9", "field10", "field11" ] 
         }
      }
  }
  </code></pre>
  
  <p>The query below doesn't return anything, but if I search within 3 fields of <code>MyType</code> everything works properly and I receive a result. </p>
  
  <pre><code>public List&lt;MyType&gt; SearchByText(String str, string[] search_fields)
  {    
      List&lt;PropertyPathMarker&gt; ppm_List = new List&lt;PropertyPathMarker&gt;();
      search_fields.ToList().ForEach(fld =&gt; ppm_List.Add(fld));
      MultiMatchQuery query = new MultiMatchQuery { Fields = ppm_List, Query = str };
      // method below doesn't return any results
      var result = es_client.Search&lt;object&gt;(s =&gt; s.Query(query)).Hits;
      ... 
  }
  </code></pre>
  
  <p>Am I wrong? If yes, where is the mistake?</p>
  
  <p><strong>Update 1:</strong></p>
  
  <p>ElasticSearch version 5.4.1, NEST version 1.5.1</p>