static Executor screenExecutor(Executor e){
  if (!useCommonPool && e == ForkJoinPool.commonPool())   return asyncPool;
  if (e == null)   throw new NullPointerException();
  return e;
}

static Executor screenExecutor ( Executor e ) { if ( ! useCommonPool && e == ForkJoinPool . commonPool ( ) ) return asyncPool ; if ( e == null ) throw new NullPointerException ( ) ; return e ; }
null - checks user executor argument , and translates uses of commonpool to asyncpool in case parallelism disabled .
