title: adding objects crash in ios
body: <p>i am trying to add an object into a nsuserdefault, but i get this crash
  "[__NSCFArray insertObject:atIndex:]: mutating method sent to immutable object"
  its crashing on this line:
  [currentFav addObject:incomingBabe];</p>
  
  <p>I have no idea why its crashing, its working on my other project.</p>
  
  <p>here is my code</p>
  
  <pre><code>-(IBAction)favorite {
      NSUserDefaults *standardDefault = [NSUserDefaults standardUserDefaults]; 
      NSMutableArray *currentFav = [[NSUserDefaults standardUserDefaults]objectForKey:@"fav"];
      NSLog(@"strings stored = %@",currentFav);
      NSMutableArray *newFav = [NSMutableArray arrayWithObject:[NSString stringWithFormat:@"bikini%02d.jpeg",self.currentNumber]];
  
  if (currentFav == NULL){
     currentFav = [[NSMutableArray alloc]init];
    }
    for(NSString *incomingBabe in newFav){
    BOOL hasStringAlready = NO;
    for(NSString *currentFavorite in currentFav){
    if([currentFavorite isEqualToString:incomingBabe]){
      hasStringAlready = YES;
      NSLog(@"has string already");
      break;
      }
    }
  if (!hasStringAlready) {
    [currentFav addObject:incomingBabe];
    hasStringAlready = YES;
    }
  }
  
   [standardDefault setObject:currentFav forKey:@"fav"];
   [standardDefault synchronize];
  }
  </code></pre>