title: $push and $set in same MongoDB update
body: <p>I'm trying to use MongoDB's Java driver to make two updates ($set and $push) to a record in the same operation.  I'm using code similar to the following:</p>
  
  <pre><code>    BasicDBObject pushUpdate = new BasicDBObject().append("$push", new BasicDBObject().append("values", dboVital));
      BasicDBObject setUpdate = new BasicDBObject().append("$set", new BasicDBObject().append("endTime", time));
      BasicDBList combinedUpdate = new BasicDBList();
      combinedUpdate.add( pushUpdate);        
      combinedUpdate.add( setUpdate);
  
  
      collection.update( new BasicDBObject().append("_id", pageId), combinedUpdate, true, false);
  </code></pre>
  
  <p>When I combine the $set and $push into the same update via a BasicDBList, I get an IllegalArgumentException: "fields stored in the db can't start with '$' (Bad Key: '$push')".</p>
  
  <p>If I make two separate updates, both pushUpdate and setUpdate produce valid results.</p>
  
  <p>Thanks!</p>