The XBM this program makes is obviously valid in some sense, but ImageMagick doesn't like it (nor does NetPBM). To fix that, write_xbm needs tweaking to replace this:

        $fh->say("static unsigned char ${indexed_name}_bits[] = { " . 
+join(', ', $hexes->@*) . ' };');
[download]

with:

        $fh->say("static unsigned char ${indexed_name}_bits[] = {");
        $fh->say(join(', ', $hexes->@*));
        $fh->say('};');
[download]