Simple NSOutlineView Retain Crash
<p>I've got a simple <code>NSOutlineView</code> setup in my OSX Swift project feeding from a basic array but its causing an <code>EXC_BAD_ACCESS</code> crash.</p>

<p>Having enabled zombies, it crashes with the following error:
<code>[NSMutableIndexSet retain]: message sent to deallocated instance</code></p>

<p>Heeeelp! Here is my code:</p>

<pre><code>class SidebarViewController: NSViewController, NSOutlineViewDataSource {

    //MARK: Vars

    @IBOutlet var sidebar : NSOutlineView?
    var data : [String] = ["Assemblies", "Parts", "Customers"]


    //MARK: Init

    override func viewDidLoad()
    {
        super.viewDidLoad()
        // Do view setup here.
    }


    //MARK: NSOutlineView Delegate / Datasource

    func outlineView(outlineView: NSOutlineView, numberOfChildrenOfItem item: AnyObject?) -&gt; Int
    {
        return data.count
    }

    func outlineView(outlineView: NSOutlineView, isItemExpandable item: AnyObject) -&gt; Bool
    {
        return false
    }

    func outlineView(outlineView: NSOutlineView, child index: Int, ofItem item: AnyObject?) -&gt; AnyObject
    {
        return data[index]
    }

    func outlineView(outlineView: NSOutlineView, objectValueForTableColumn tableColumn: NSTableColumn?, byItem item: AnyObject?) -&gt; AnyObject?
    {
        return item
    }
}
</code></pre>