'_' is not convertible to 'String'

Question

I'm trying to create a dictionary of attributes to pass into NSString.drawInRect . However, Swift won't let me, as the following code results in mysterious error message '_' is not convertible to 'String'

let font = NSFontManager.sharedFontManager().fontWithFamily(...)
let color = NSColor.whiteColor() 
let paragraphStyle = NSParagraphStyle.defaultParagraphStyle()
let attributes = [
    NSParagraphStyleAttributeName: paragraphStyle,
    NSFontAttributeName: font,
    NSForegroundColorAttributeName: color]

What needs to be done differently?

Answer 1

(This answer add nothing new to matt's answer so if you upvote this, remember to upvote his as well)

font is optional, you can unwrap it with font! , like this:

let font = NSFontManager.sharedFontManager().fontWithFamily(...)
let color = NSColor.whiteColor() 
let paragraphStyle = NSParagraphStyle.defaultParagraphStyle()
let attributes = [
    NSParagraphStyleAttributeName: paragraphStyle,
    NSFontAttributeName: font!,
    NSForegroundColorAttributeName: color]

Answer 2

font is an Optional. Unwrap it to get the font that's wrapped inside it.