Method onException

future-java/src/main/java/io/trane/future/Promise.java:786–789

(final Throwable ex)

    final Responder<T> r = new Responder<T>() {
      @Override
      public final void onException(final Throwable ex) {
        p.setException(ex);
      }

      @Override
      public final void onValue(final T value) {