code: @CheckReturnValue
      @SchedulerSupport(SchedulerSupport.NONE)
      public static <T> Single<T> just(final T item) {
          ObjectHelper.requireNonNull(item, "value is null");
          return RxJavaPlugins.onAssembly(new SingleJust<T>(item));
      }
docs: Returns a {@code Single} that emits a specified item.
  <p>
  <img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.just.png" alt="">
  <p>
  To convert any object into a {@code Single} that emits that object, pass that object into the
  {@code just} method.
  <dl>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code just} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  
  @param item
  the item to emit
  @param <T>
  the type of that item
  @return a {@code Single} that emits {@code item}
  @see <a href="http://reactivex.io/documentation/operators/just.html">ReactiveX operators documentation: Just</a>