Pull request to master

You can override the accessor methods for these properties instead so that even if you access one of them in any part of the code (not just in `viewDidLoad`), it ensures that they will always return an instantiated array.

e.g.
```
- (NSMutableArray *)enemies
{
   if (_enemies == nil) {
      _enemies = [[NSMutableArray alloc] init];
   }

   return _enemies;
}
```

When you've implemented these methods, there will be no need for lines 111 - 118. :)