my $paths = join "\0", @_;
  $paths .= "\0\0";

##</code><code>##

  my $paths = join "\0", @_, "\0";

##</code><code>##

johngg@aleatico:~$ perl -Mstrict -Mwarnings -E '
my @p = qw{ a b c };
my $p = join "\0", @p, "\0";
print $p;' | hexdump -C
00000000  61 00 62 00 63 00 00                              |a.b.c..|
00000007