title: Importing ObjectID as string
body: <p>I am trying to upgrade a Solr 6.2.1 single node instance to a SolrCloud setup using the Solr version 6.6. The issue I am facing is that while performing data import from mongodb using the solr-mongo-importer-1.1.0.jar and mongo-java-driver-2.14.3.jar, the _id field is being imported as <code>"_id":"org.bson.types.ObjectId:585a53d109ed44343743ebd1"</code> instead of <code>"_id":"585a53d109ed44343743ebd1"</code> as in the Solr 6.2.1 instance. (The jars are the same version in both the cases)</p>
  
  <p>The schema contains the following (same in both versions):</p>
  
  <pre><code>&lt;fieldType name="string" class="solr.StrField"sortMissingLast="true"/&gt;
  &lt;field name="_id" type="string" indexed="true" stored="true"/&gt;
  </code></pre>
  
  <p>Is there any change in the fieldType in the new version or am I missing something?</p>