src/main/java/io/reactivex/Maybe.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Maybe<T> fromSingle(SingleSource<T> singleSource) {
        ObjectHelper.requireNonNull(singleSource, "singleSource is null");
        return RxJavaPlugins.onAssembly(new MaybeFromSingle<T>(singleSource));
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Maybe<T> fromSingle(SingleSource<T> singleSource) {
        ObjectHelper.requireNonNull(singleSource, "singleSource is null");
        return RxJavaPlugins.onAssembly(new MaybeFromSingle<T>(singleSource));
    }
Wraps a SingleSource into a Maybe.

<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code fromSingle} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param <T> the target type
@param singleSource the SingleSource to convert from
@return the new Maybe instance
@throws NullPointerException if single is null