c:\@Work\Perl\monks>perl -wMstrict -e
"use Data::Dump qw(dd);
 ;;
 my @sorted = sort { dd $a, $b;  $a cmp $b; } (qw(d a c e b), undef);
 dd \@sorted;
"
("d", "a")
("c", "e")
("b", undef)
Use of uninitialized value in string comparison (cmp) at -e line 1.
("a", "c")
("c", "d")
("d", "e")
("a", undef)
Use of uninitialized value in string comparison (cmp) at -e line 1.
("a", "b")
("c", "b")
[undef, "a", "b", "c", "d", "e"]