title: How to solve "Expected element name to be '_t', not 'number'."
body: <p>I have a mongo model like this:</p>
  
  <pre><code>class ObjectA {
          [BsonId(IdGenerator = typeof(BsonObjectIdGenerator))]
          public BsonObjectId Id;
  
          [BsonElement("number")]
          public int Number { get; set; }
  
          [BsonElement("b")]
          public List&lt;ObjectB&gt; objectB { get; set; }
  }
  
  class ObjectB {
          [BsonElement("someProperty")]
          public string SomeProperty { get; set; }
  }
  </code></pre>
  
  <p>My problem is when I aggregate the collection with <code>{$unwind:objectB}</code>. The result documencts have a unique object on the property <code>objectB</code> (not a list). 
  So the cast failes with the exception:</p>
  
  <blockquote>
    <p>An error occurred while deserializing the ObjectB property of class
    ObjectA: Expected element name to be '_t', not
    'number'.</p>
  </blockquote>
  
  <p>Do I have to create a new model for this or is there a easier way to solve it?</p>