PHP7致命错误：Switch语句只能包含一个默认子句

I'm debugging a PHP5->7 upgrade and got the following error on this block of code:

PHP7 Fatal error: Switch statements may only contain one default clause

function adserve_cache_get_cache($data = NULL) {
  static $cache = NULL;
  // if we don't the the cache yet, build it
  if (is_null($cache)) {
    $cache = module_invoke_all('ad_build_cache');
  }

  if ($data) {
    if (isset($cache[$data])) {
      return $cache[$data];
    }
    else {
      return NULL;
    }
  }
  return $cache;
}

The error was generated using the phpmar tool.

I'm wondering if it's a false positive based on this comment code:

/**
 * Build and return the cache.
 * TODO: It's expensive to build the cache each time we serve an ad, this should
 * be cached in the database, not in a static.
 */

Any help would be appreciated.