The Subscriptions form element is displayed even if there is nothing to subscribe to. The solution is simple, add an is_array() check, as below:

125 if(is_array($options)) {

126 $form['mailout'] = array(
127 '#type' => 'checkboxes',
128 '#options' => $options,
129 '#title' => t('Subscriptions'),
130 );

131 }

Regards,
Gábor