Merge "MediaSession2: Fix random NPE in MediaBrowser2Test" into pi-dev

    /**

     * Get instance of the {@link MediaSession2} that you've previously created with the

     * {@link #onCreateSession} for this service.

     * <p>

     * This may be {@code null} before the {@link #onCreate()} is finished.

     *

     * @return created session

     */

    public final MediaSession2 getSession() {

    public final @Nullable MediaSession2 getSession() {

        return mProvider.getSession_impl();

    }