static Executor screenExecutor(Executor e) {
    if (!USE_COMMON_POOL && e == ForkJoinPool.commonPool())
      return ASYNC_POOL;
    return Objects.requireNonNull(e);
  }
static Executor screenExecutor ( Executor e ) { if ( ! USE_COMMON_POOL && e == ForkJoinPool . commonPool ( ) ) return ASYNC_POOL ; return Objects . requireNonNull ( e ) ; }
Null-checks user executor argument, and translates uses of commonPool to ASYNC_POOL in case
parallelism disabled.