Creating nullable class
<p>How do I create a nullable (?) class in C#? Like:</p>

<pre><code>public class Hello1 {
  public int Property1 { get; set; }
}

public class Hello2 {
 Public Hello1? Property2 { get; set; } //Hello1 should work when it has "?"
}
</code></pre>

<p>I wanna make Hello1 class to take the form "Hello1?" if needed.</p>
