I couldn't turn up any great links on the subject, but Objective-C (as used in Apple's Cocoa development) uses this pattern. Calling a method on a nil object returns nil. It'd be similar to this Perl, which would print undefined:

# this would work if it were Objective-C
# using Perl's syntax
my $foo    = undef;
my $result = $foo->message;
print "undefined\n"
    if not defined $result;
[download]

I happen to like it.