Modify stringValue of NSTextField in Swift

I am trying to change the content of NSTextField in the ViewController by changing its stringValue coming from AppDelegate, but it gives me an error.

The code in AppDelegate is:

class AppDelegate: NSObject, NSApplicationDelegate {

    var consoleOutput:String? = "Console Output"

    func executeCommand(command: String, args: [String]) -> String {

        let task = NSTask()
        task.launchPath = command
        task.arguments = args

        let pipe = NSPipe()
        task.standardOutput = pipe
        task.launch()

        let data = pipe.fileHandleForReading.readDataToEndOfFile()
        let output:String = NSString(data: data, encoding: NSUTF8StringEncoding)!
        consoleOutput = output
        return output
    }
}

It is called from the ViewController:

var myDelegate = NSApplication.sharedApplication().delegate! as AppDelegate

and the NSTextField is an IBOutlet created earlier:

@IBOutlet weak var outputText: NSTextField!

and tried to modify later:

outputText.stringValue = myDelegate.consoleOutput!

But all I get is

fatal error: unexpectedly found nil while unwrapping an Optional value

What am I doing wrong?

Try setting this line: let output:String = NSString(data: data, encoding: NSUTF8StringEncoding)!to: let output: String = "Test" If this eliminates the error, then you know that NSString(data: data, encoding: NSUTF8StringEncoding) is returning nil, so something is wrong with the data pipe.