title: DefaultIfEmpty doesn't work
body: <p>Why is  array still null after queried by DefaultIfEmpty ? </p>
  
  <pre><code>class Program
  {
      static void Main(string[] args)
      {
          Program[] array = new Program[5];
          Program[] query = array.DefaultIfEmpty(new Program()).ToArray();
          foreach (var item in query)
          {
              Console.WriteLine(item.ToString());
          }
          Console.ReadKey();
      }
  }
  </code></pre>