Another slight variation on a custom sort sub:

c:\@Work\Perl\monks>perl -le
"use warnings;
 use strict;
 ;;
 use Test::More 'no_plan';
 use Test::NoWarnings;
 ;;
 my $OptOrd = 1;
 ;;
 my $Test = [
   [  1, 'c'   ],
   [  2, 'a'   ],
   [  3, ''    ],
   [  4, undef ],
   [  5, 'foo' ],
   [  6, ''    ],
   [  7, 'cee' ],
   [  8, undef ],
   [  9, 'tee' ],
   [ 10, 't'   ],
   ];
 ;;
 my $Expected = [
   [  3, ''    ],
   [  6, ''    ],
   [  2, 'a'   ],
   [  1, 'c'   ],
   [  7, 'cee' ],
   [  5, 'foo' ],
   [ 10, 't'   ],
   [  9, 'tee' ],
   [  4, undef ],
   [  8, undef ],
   ];
 ;;
 my @got = sort by_deaccented_ascending_with_undef_highest @$Test;
 ;;
 is_deeply \@got, $Expected, 'custom sort sub';
 ;;
 done_testing;
 ;;
 sub deaccent { return $_[0]; }
 ;;
 sub by_deaccented_ascending_with_undef_highest {
   my ($aa, $bb) = ($a->[$OptOrd], $b->[$OptOrd]);
   ;;
   return defined  $aa  &&  defined  $bb
        ? deaccent($aa) cmp deaccent($bb)
        : defined  $bb  cmp defined  $aa
        ;
   }
"
ok 1 - custom sort sub
1..1
ok 2 - no warnings
1..2
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defined returns '' (empty string) for undefined, 1 for defined, and '' will lexically cmp below 1.