"Can't create new document" alert unwanted

FROM : Kaspar Fischer
DATE : Thu Dec 23 17:52:43 2004

Dear all,

In a newly created Cocoa project I have added code to the
-(id)init method of MyDocument. It is suggested there that I
should

  // Add your subclass-specific initialization here.
  // If an error occurs here, send a [self release] message
  // and return nil.

So I did. I ask the user some details, and if she aborts,
I return nil. Then however, an alert appears saying

    NEW
    Can’t create new document.

Clearly, when the user aborts, there is no need to show
such a beast anymore. How can I get rid of it?

Thanks a lot,
Kaspar

P.S. This question has been asked before, see

  http://lists.apple.com/archives/cocoa-dev/2002/Dec/msg00294.html

but nobody seems to have answered.