        if (sourceIndex == NSNotFound) {     dispatch_async(dispatch_get_main_queue(), ^{ if (block) block([NSError spotifyErrorWithCode:SP_ERROR_INVALID_INDATA]); });     return;    }        NSInteger destinationIndex = [self indexInFlattenedListForIndex:newIndex inFolder:aParentFolderOrNil];        if (destinationIndex == NSNotFound) {     dispatch_async(dispatch_get_main_queue(), ^{ if (block) block([NSError spotifyErrorWithCode:SP_ERROR_INDEX_OUT_OF_RANGE]); });     return;    }        