title: Mongoose Populate not working with Array of ObjectIds
body: <p>Here is my schema:</p>
  
  <pre><code>/** Schemas */
  var profile = Schema({
      EmailAddress: String,
      FirstName: String,
      LastName: String,
      BusinessName: String
  });
  
  var convSchema = Schema({
      name: String,
      users: [{
          type: Schema.Types.ObjectId,
          ref: 'Profiles'
      }],
      conversationType: {
          type: String,
          enum: ['single', 'group'],
          default: 'single'
      },
      created: {
          type: Date,
          default: Date.now
      },
      lastUpdated: {
          type: Date,
          default: Date.now
      }
  });
  
  /** Models */
  db.Profiles = mongoose.model('Profiles', profile);
  db.Conversations = mongoose.model('ChatConversations', convSchema);
  
  module.exports = db;
  </code></pre>
  
  <p>Then I try to populate Users using following code (<a href="http://mongoosejs.com/docs/populate.html" rel="nofollow">http://mongoosejs.com/docs/populate.html</a>):</p>
  
  <pre><code>db.Conversations.find(query).populate('users').exec(function (err, records)     {
      console.log(records);
  });
  </code></pre>
  
  <p>This is returning <code>records</code> but <code>users</code> array as a blank array <code>[]</code>. </p>
  
  <p>I also tried the other way around (<a href="http://mongoosejs.com/docs/api.html#model_Model.populate" rel="nofollow">http://mongoosejs.com/docs/api.html#model_Model.populate</a>):</p>
  
  <pre><code>db.Conversations.find(query, function (err, records) {
      db.Conversations.populate(records, {path: "users", select: "BusinessName"}, function (err, records) {
          console.log(records);
      });
  });
  </code></pre>
  
  <p>Results are same. When I checked references into profile collection records are there.</p>
  
  <p>Any idea what wrong here?</p>