Swift, NSOutlineView, and EXC_BAD_ACCESS...

Hey All,

I've got a pretty basic NSOutlineView going as I try and learn AppKit and Mac dev, my "Object Value for Table Column" is giving me some headache.

    var rootURL = NSURL(fileURLWithPath: "/");
  
    var rootItem:FileSystemItem! = nil;
    convenience init(withRootURL url:NSURL)
    {
        self.init()
        self.rootURL = url;
        self.rootItem = FileSystemItem(withURL: url)
    }
  
    func outlineView(outlineView: NSOutlineView, numberOfChildrenOfItem item: AnyObject?) -> Int {
        var fileItem = item as? FileSystemItem;
        if fileItem == nil {
            fileItem = self.rootItem;
        }
        return fileItem?.numberOfChildren() ?? 1;
    }
  
    func outlineView(outlineView: NSOutlineView, isItemExpandable item: AnyObject) -> Bool {
        let fileItem = item as? FileSystemItem;
        let numChildren = fileItem?.numberOfChildren();
        return numChildren > 0 ? true : false;
    }
  
    func outlineView(outlineView: NSOutlineView, child index: Int, ofItem item: AnyObject?) -> AnyObject {
        let fileItem = item as? FileSystemItem;
        return fileItem?.childAtIndex(index) ?? self.rootItem.childAtIndex(index)!;
    }
  
    func outlineView(outlineView: NSOutlineView, objectValueForTableColumn tableColumn: NSTableColumn?, byItem item: AnyObject?) -> AnyObject? {
      
        if let theItem = item
        {
            if let fileItem = theItem as? FileSystemItem   <-----------EXC_BAD_ACCESS
            {
                return fileItem.fileURL.lastPathComponent
            }
        }
      
        return "Empty?"
    }

I've indicated above where I'm getting a BAD_ACCESS error. This usually means something that's deallocated is being referenced, but how could the item passed in by the framework be deallocated?

Now, NSOutlineViews have confused the heck out of me with how they pass "nil" in for the "items" sometimes. This definitely happens on the initial "Number of Children for Item" Check. It's assumed that an inquiry with a nil item is representative of the "root item". Is this also true for the child of item call?