code: @NotNull
  	public static Promise<Void> sequence(@NotNull Iterator<? extends Promise<Void>> promises) {
  		return Promise.ofCallback(cb ->
  				sequenceImpl(promises, cb));
  	}
docs: Calls every {@code Promise} from {@code promises} in sequence and discards
  their results.Returns a {@code SettablePromise} with {@code null} result as
  a marker when all of the {@code promises} are completed.
  
  @return {@code Promise} that completes when all {@code promises} are completed