userpoints_nodelimit return empty page

when userpoints is active and user total points is not enough, the form return empty page.

i found the problem is at the userpoints_nodelimit.module

$form = NULL;

i try to change it to

$form = NULL;
$form['dummy'] = array(
  '#default_value' => '',
  '#type' => 'hidden'
);

and now it works!