An empty return statement would be a mistake there, precisely because the function might be called in list context. In Perl, list context is sometimes inconvenient to avoid, for example if an expression happens to be used as a subroutine argument. We should not expect our undef function result to vanish and be replaced by the next argument in such a situation, I think.

The only time where this would harm the code I tend to write is if I had a semi-predicate problem in a function that returned a list. (The only reason I don't run into the problem where hash declarations impose list context is that I don't do much CGI programming, where I might call $q->param( 'foo' ) in a hash assignment.)