array_merge(): Argument #2 is not an array

My dblog is full of PHP errors like this:

array_merge() [<a href='function.array-merge'>function.array-merge</a>]: Argument #2 is not an array in /var/www/drupal-6.14/sites/all/modules/coder/coder.module on line 1495.

line 1495 of coder.module is:

  $allowed_extensions = array_merge($coder_args['#php_extensions'], $coder_args['#include_extensions'], array('module'));