I believe this message is cause by the warning's pragma (-w), to alert you to the printing of an undefined value, not the returning of one. To test this thoery, i used the following :

#!/usr/bin/perl -wl
use strict;

my $hashref = { foo => { bar => 'xyzzy' } };

sub name_me {
    # Note: there is no $hashref->{foo}{foo}
    return \ $hashref->{foo}{foo};
}

$a = name_me();

print $a;

print $$a;

print ${ name_me() }
[download]

This, on my machine, prints the following :

SCALAR(0x184068)
Use of uninitialized value in print at bar.pl line 15.

Use of uninitialized value in print at bar.pl line 17.
[download]

---

$ perl -e 'do() || ! do() ;'
Undefined subroutine &main::try
[download]