Undefined index: render element in theme() when displaying FB login form

When displaying the FB login form for users that aren't logged into FB already, I got the following error
Undefined index: render element in theme()...

Patch suggestion:

Change line 549
$fb_button = theme('fb_login_button', t(_fb_user_button_text($form_id)), array('form_id' => $form_id));
to
$fb_button = theme('fb_login_button', array('text' => t(_fb_user_button_text($form_id)), 'form_id' => $form_\
id));