title: MongoDB java Driver query on nested object using objectID is not working
body: <p>I have following mongodb document structure</p>
  
  <pre><code>{
      "_id": ObjectId("571530da41995a703faaf55b"),
      "project_name": "abc",
      "status": "new",
      "cluster": "",
      "sku": {
          "_id": "57152f7941995a703faaf559",
          "name": "temp",
          "distribution": "apache",
          "creation_date": "2016-04-18T19:02:46.595Z",
          "user_id": "570784b1682d25f45b64ed51",
          "__v": 0,
          "services": []
      }
  }
  </code></pre>
  
  <p>I want to find project info given a sku._id. I am using following piece of code for this purpose.</p>
  
  <pre><code>String  getProjectIDforSku(String skuID ) {
          ObjectId id = new ObjectId(skuID);
          BasicDBObject query = new BasicDBObject("sku", new BasicDBObject("_id", skuID));
          DBObject obj = getCollection("deployment", "projects").findOne(query);
          if (obj != null) {
              var jsonString = Json.parse(obj.toString());
              return jsonString;
          } else
              return null;
      }
  </code></pre>
  
  <p>When I call this function, I receive null instead of valid json string. 
  Can anyone guide me where i am wrong?
  Thanks</p>