WSOD: PHP Fatal error: Unsupported operand types in rules.module on line 234

After enabling modules i get:
PHP Fatal error: Unsupported operand types in /var/www/virtual/renner/html/development/code/sites/all/modules/rules/rules.module on line 234

Digging the source shows $data[$hook] is not initialized so under rare circumstances this can kill our installation.

function rules_fetch_data($hook) {
  $data = &drupal_static(__FUNCTION__, array());
  static $discover = array(
    'action_info' => 'RulesActionHandlerInterface',
    'condition_info' => 'RulesConditionHandlerInterface',
    'event_info' => 'RulesEventHandlerInterface',
  );

  if (!isset($data[$hook])) {
    foreach (module_implements('rules_' . $hook) as $module) {
      $result = call_user_func($module . '_rules_' . $hook);
      if (isset($result) && is_array($result)) {
        foreach ($result as $name => $item) {
          $item += array('module' => $module);
          $data[$hook][$name] = $item;
        }
      }
    }
    // Support class discovery.
    if (isset($discover[$hook])) {
      $data[$hook] += rules_discover_plugins($discover[$hook]);   // *** That's the offending line ***
    }
    drupal_alter('rules_'. $hook, $data[$hook]);
  }
  return $data[$hook];
}