code: func (w *KeyedValue) ValueOk(k string) (interface{}, bool) {
  	w.lock.Lock()
  	defer w.lock.Unlock()
  
  	v, val := w.valueWaiter(k)
  	return v, val == nil
  }
docs: // ValueOk gets the value for the given key, returning immediately if the
  // value doesn't exist. The second return argument is true if the value exists.