private void fireHandler() {
        if (handler != null) {
            if (succeeded) {
                handler.handle(AsyncResultImpl.create(result));
            } else {
                handler.handle(AsyncResultImpl.create(error));
            }
        }
    }
@author Marc Savy {@literal <msavy@redhat.com>}
@param <T> the contained type
gateway/engine/core/src/main/java/io/apiman/gateway/engine/async/AsyncFutureImpl.java