code: public static <R, T> Transformer<T, R> ignoreElementsThen(final Observable<R> next) {
          return new Transformer<T, R>() {
  
              @SuppressWarnings("unchecked")
              @Override
              public Observable<R> call(Observable<T> source) {
                  return ((Observable<R>) (Observable<?>) source.ignoreElements()).concatWith(next);
              }
          };
      }
docs: <p>
  Returns an observable that subscribes to {@code this} and wait for
  completion but doesn't emit any items and once completes emits the
  {@code next} observable.
  
  <p>
  <img src=
  "https://github.com/davidmoten/rxjava-extras/blob/master/src/docs/ignoreElementsThen.png?raw=true"
  alt="marble diagram">
  
  @param <R>
  input observable type
  @param <T>
  output observable type
  @param next
  observable to be emitted after ignoring elements of
  {@code this}
  @return Transformer that applied to a source Observable ignores the
  elements of the source and emits the elements of a second
  observable