Warning Message Appearing About Parameter

I keep having this warning message appear.

Warning: in_array() expects parameter 2 to be array, null given in lessc_parser->openString() (line 2575 of /Users/myuser/Sites/mytheme/public_html/sites/all/libraries/lessphp/lessc.inc.php).

I was using an older version of LESS and thought that upgrading would solve it but the problem persists.

Has anyone ran across this in the past? When I go to that file I don't notice anything unusual going on.

This is the array at line 2575.

if (in_array($tok, $rejectStrs)) {
	$count = null;
	break;
}