Error: Argument #1 is not an array in noindex_external_links.module on line 153.

After installing and enabling an input format provided by this module getting the following error

warning: array_diff() [function.array-diff]: Argument #1 is not an array in C:\wamp\www\kopsite\sites\all\modules\noindex_external_links\noindex_external_links.module on line 153.

The module seems works as expected but these errors always displayed on front-end.

Running drupal 6.19

Thanks in advise