Document that WallpaperManager.getDrawable() can return null

     * This is returned as an

     * abstract Drawable that you can install in a View to display whatever

     * wallpaper the user has currently set.

     *

     * @return Returns a Drawable object that will draw the wallpaper.

     * <p>

     * This method can return null if there is no system wallpaper available, if

     * wallpapers are not supported in the current user, or if the calling app is not

     * permitted to access the system wallpaper.

     *

     * @return Returns a Drawable object that will draw the system wallpaper,

     *     or {@code null} if no system wallpaper exists or if the calling application

     *     is not able to access the wallpaper.

     */

    public Drawable getDrawable() {

        Bitmap bm = sGlobals.peekWallpaperBitmap(mContext, true, FLAG_SYSTEM);