I got error “SIGABRT” goal, I’m not white? Why. . . Please try to h * lp me

I was programming and I got the error “SIGABRT”… But I don’t know why

Please try to help me, I will be very happy

in this code is “SIGABRT”:

-(void)list
{
    NSLog(@"===List of songs===");
    for (Song *theSong in playlist)
    {   NSLog(@"Title:'%@'",theSong.title); //SIGABRT ERROR
        NSLog(@"Artist:'%@'",theSong.artist);
        NSLog(@"Album:'%@'",theSong.album);
        NSLog(@"-------NEXT SONG-------");}
}

and in my main.m I got that error after writing this:

    Playlists *searchRes;
    searchRes = [playlistNow lookup:@"In"];
    [searchRes list];

For lookup method code is this:

    -(Playlists *)lookup:(NSString *)theTitle
{
    Playlists *result = [[Playlists alloc]initWithName:@"results"];
    for (Song *theSong in playlist)
    {
        if([theSong.title rangeOfString:theTitle options:NSCaseInsensitiveSearch].location != NSNotFound)
        {
            [result addSong:theTitle];
        }
    }
    return result;
}