operator "??" in Unity 4.3

Why the operator C# "??" has stopped working after update to Unity 4.3

this code:

Code (csharp):

1. var boxColider = gameObject.GetComponent<BoxCollider> () ?? gameObject.AddComponent<BoxCollider> ();

not work.

this code:

Code (csharp):

1.  
2. if (gameObject.GetComponent<BoxCollider> () == null) {
3.     var boxColider = gameObject.AddComponent<BoxCollider> ();
4. }
5.  

work.