Thanks for your input, though I should have specified one thing more clearly: when I said I return (undef), I meant that I just return;, I don't return undef;. I'm aware of the problem with returning undef explicitly.

(For the unaware: a bare return gives the caller an undef, regardless of whether the call was in scalar or list context. Returning an explicit undef gives the caller undef in scalar context and a list containing one element (undef) in list context.)