Yeah, only runnable code that proves the complaint proves it, so counter proof

use strict;
use warnings;
my $foo;
my $bar = 0;
my $baz = '0';
for my $arg ( $baz, $bar, $foo ){
    use Data::Dump;
    dd( $arg );
    print qq{ the $arg\n };
}
__END__
0
 the 0
 0
 the 0
 undef
Use of uninitialized value $arg in concatenation (.) or string at - li
+ne 9.
 the
[download]

So there you have it 0 is a perlnumber, your problem is that you don't have 0, you have under