code: public static <T> CompletableFuture<T> toCompletableFuture(Single<T> single) {
          return Java8FutureUtils.createCompletableFuture(RxJava2FutureUtils.createValueSource(single));
      }
docs: Converts {@link io.reactivex.Single} to {@link java.util.concurrent.CompletableFuture}.