Beware: Despite the docs SKNode userData is optional

In the Swift documentation for SKNode the userData member (a dictionary) is defined as follows:

userData

A dictionary containing arbitrary data.

Declaration

SWIFT

var userData: NSMutableDictionary!

OBJECTIVE-C

@property(nonatomic, retain) NSMutableDictionary *userData

However, in Objective-C the userData member is initially nil. Given that this is the same class then it should also be in Swift and using it, e.g.

let node = SKSpriteNode(imageNamed: name)

node.userData["action"] = Action() // custom class

causes a crash:

fatal error: Can't unwrap Optional.None

This is because the it is in fact nil despite the '!' following the Swift definition. This must be a documentation bug. The correct code is:

let node = SKSpriteNode(imageNamed: name)

node.userData = NSMutableDictionary()

node.userData["action"] = Action() // custom class