/**
  * Manage checkboxes on event save.
  * When an event is saved on the event screen and a checkbox is not checked,
  * no value is posted and therefore the event meta key is not updated.
  *
  * @params	obj		$post	The events WP_POST object
  * @return	void
  */
 function manage_custom_fields_on_event_save($post)
 {
     $mdjm_event = new MDJM_Event($post->ID);
     $query = mdjm_get_custom_fields();
     $custom_fields = $query->get_posts();
     foreach ($custom_fields as $custom_field) {
         if ('checkbox' != get_post_meta($custom_field->ID, '_mdjm_field_type', true)) {
             continue;
         }
         $key = '_mdjm_event_' . str_replace('-', '_', $custom_field->post_name);
         if ($mdjm_event->get_meta($key) && empty($_POST[$key])) {
             $meta[$key] = '';
         }
     }
     if (!empty($meta)) {
         mdjm_update_event_meta($mdjm_event->ID, $meta);
     }
 }