title: mongoose is removing empty object out of embedded documents in array
body: <p>notice the following code, that shows a schema with 2 arrays, one is configured to be from Type: </p>
  
  <pre><code>[
    mongoose.Schema.Types.Mixed
  ]
  </code></pre>
  
  <p>and one is configured to be from type:</p>
  
  <pre><code>[
   {
     value: mongoose.Schema.Types.Mixed
   }
  ]
  </code></pre>
  
  <p>Here is the code: </p>
  
  <pre><code>var mongoose = require('mongoose');
  mongoose.connect('mongodb://localhost/test');
  var schema  = new mongoose.Schema({
    withSchema:    [{  
      value:mongoose.Schema.Types.Mixed}
    ],  
    withoutSchema: [mongoose.Schema.Types.Mixed],
  } , {minimize: false});
  var Tweak = mongoose.model('tweak', schema );
  </code></pre>
  
  <p>I update the document using the same data:</p>
  
  <pre><code>var data = { 
    "withSchema"    : [ { "value": { a:"221", b:{} } } ],
    "withoutSchema" : [ { "value": { a:"221", b:{} } } ] 
  } 
  Tweak.findByIdAndUpdate("545680170960023a185ea77e", data, function(err, doc){
    console.log(doc);
    //{ 
    // "withSchema"    : [ { "value": { a:"221" } } ],
    // "withoutSchema" : [ { "value": { a:"221", b:{} } } ] 
    //} 
  });
  </code></pre>
  
  <p>How do I prevent this b:{} removal? </p>
  
  <p><strong>EDIT</strong>:</p>
  
  <p>It turns out this happens only when there is an embeddedDocument inside an Array.</p>