src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> wrap(ObservableSource<T> source) {
        ObjectHelper.requireNonNull(source, "source is null");
        if (source instanceof Observable) {
            return RxJavaPlugins.onAssembly((Observable<T>)source);
        }
        return RxJavaPlugins.onAssembly(new ObservableFromUnsafeSource<T>(source));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> wrap(ObservableSource<T> source) {
        ObjectHelper.requireNonNull(source, "source is null");
        if (source instanceof Observable) {
            return RxJavaPlugins.onAssembly((Observable<T>)source);
        }
        return RxJavaPlugins.onAssembly(new ObservableFromUnsafeSource<T>(source));
    }
Wraps an ObservableSource into an Observable if not already an Observable.

<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code wrap} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <T> the value type
@param source the source ObservableSource instance
@return the new Observable instance or the same as the source
@throws NullPointerException if source is null