How to get stringValue from a NSTextView

I am creating a OSX Cocoa Application using Swift. I am trying to get the input from a NSTextView to my paste board.

@IBOutlet var issues: NSTextView!

@IBAction func button(_ sender: Any) {
    let stringvalue = "Issue: \(issues.StringValue)"
    let pasteboard = NSPasteboard.general()
    pasteboard.declareTypes([NSPasteboardTypeString], owner: nil)               
    pasteboard.setString(stringvalue, forType: NSPasteboardTypeString)
}

The only error that I am getting is "Value of type 'NSTextView' has no member 'stringValue'.

I don't want to use NSTextField since that only lets me use one line.