src/main/java/javascalautils/concurrent/FutureImpl.java
private <R> void notifyHandlers() {
        // the response may or may not exist at this point
        response.forEach(t -> eventHandlers.stream().forEach(h -> h.notify(t)));
    }
private <R> void notifyHandlers() {
        // the response may or may not exist at this point
        response.forEach(t -> eventHandlers.stream().forEach(h -> h.notify(t)));
    }
Invoke all handlers with the value of this Future. <br>
The response may or may not exist at this point. <br>
A filter is applied to make sure we only notify handlers that have not been notified before.