code: @CheckReturnValue
      @BackpressureSupport(BackpressureKind.FULL)
      @SchedulerSupport(SchedulerSupport.NONE)
      public final Flowable<T> repeatUntil(BooleanSupplier stop) {
          ObjectHelper.requireNonNull(stop, "stop is null");
          return RxJavaPlugins.onAssembly(new FlowableRepeatUntil<T>(this, stop));
      }
docs: Returns a Flowable that repeats the sequence of items emitted by the source Publisher until
  the provided stop function returns true.
  <p>
  <img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/repeat.on.png" alt="">
  <dl>
  <dt><b>Backpressure:</b></dt>
  <dd>The operator honors downstream backpressure and expects the source {@code Publisher} to honor backpressure as well.
  If this expectation is violated, the operator <em>may</em> throw an {@code IllegalStateException}.</dd>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code repeatUntil} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  
  @param stop
  a boolean supplier that is called when the current Flowable completes and unless it returns
  false, the current Flowable is resubscribed
  @return the new Flowable instance
  @throws NullPointerException
  if {@code stop} is null
  @see <a href="http://reactivex.io/documentation/operators/repeat.html">ReactiveX operators documentation: Repeat</a>