code: public static <E> java.util.function.Function<CompletionStage<E>, Flowable<E>> completionStageToPublisher() {
        return (java.util.function.Function) completionStageToPublisher;
     }
docs: Provides an interop function that can be used to convert a CompletionStage into a Flowable. Note that this function
  is from the standard java.util.function package since we don't want the method to throw an exception
  <p>
  Remember that the CompletionStage when completing normally <b>MUST</b> have a non null value!
  @param <E> underlying type
  @return java.util function to convert CompletionStage to Flowable