src/main/java/io/reactivex/Single.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Disposable subscribe(Consumer<? super T> onSuccess) {
        return subscribe(onSuccess, Functions.ON_ERROR_MISSING);
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Disposable subscribe(Consumer<? super T> onSuccess) {
        return subscribe(onSuccess, Functions.ON_ERROR_MISSING);
    }
Subscribes to a Single and provides a callback to handle the item it emits.
<p>
If the Single emits an error, it is wrapped into an
{@link io.reactivex.exceptions.OnErrorNotImplementedException OnErrorNotImplementedException}
and routed to the RxJavaPlugins.onError handler.
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code subscribe} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param onSuccess
the {@code Consumer<T>} you have designed to accept the emission from the Single
@return a {@link Disposable} reference can request the {@link Single} stop work.
@throws NullPointerException
if {@code onSuccess} is null
@see <a href="http://reactivex.io/documentation/operators/subscribe.html">ReactiveX operators documentation: Subscribe</a>