title: Can’t merge a non object mapping with an object mapping error in machine learning(beta) module
body: <p>I'm trying out the new machine learning module in x pack. I'm trying to identify rare response codes in HTTP Access logs in time. My logs are being stored in elasticsearch as below:</p>
  
  <pre><code>{
    "_index": "logstash-2017.05.18",
    "_type": "Accesslog",
    "_id": "AVxvVfFGdMmRr-0X-J5P",
    "_version": 1,
    "_score": null,
    "_source": {
      "request": "/web/Q123/images/buttons/asdf.gif",
      "server": "91",
      "auth": "-",
      "ident": "-",
      "verb": "GET",
      "type": "Accesslog",
      "path": "/path/to/log",
      "@timestamp": "2017-05-18T10:20:00.000Z",
      "response": "304",
      "clientip": "1.1.1.1",
      "@version": "1",
      "host": "ip-10-10-10-10",
      "httpversion": "1.1",
      "timestamp": "18/May/2017:10:20:00 +0530"
    },
    "fields": {
      "@timestamp": [
        1495102800000
      ]
    }
  </code></pre>
  
  <p>I added a detector where I selected the function as 'rare' and the by_field_name' as 'response'. But when I save the job I get the following error:</p>
  
  <pre><code>Save failed: [illegal_argument_exception] Can't merge a non object mapping [response] with an object mapping [response]
  </code></pre>
  
  <p>Please help.</p>