Swift 2.2 check string or int for nil

Question

I just studied new language for myself - swift, and now i'm stuck on trouble with empty values. I write simple app that searches min and max of an array. But if enter empty values in app - crush will happen with error: fatal error: unexpectedly found nil while unwrapping an Optional value (lldb)

I tried to implement some checks on nil and isEmpty, but app is still crushing.

Here is the code:

 import Cocoa

class ViewController: NSViewController {


    @IBOutlet weak var inputArrayValues: NSTextField!
    @IBOutlet weak var minLabel: NSTextField!
    @IBOutlet weak var maxLabel: NSTextField!
    @IBAction func arrayMinMax(sender: AnyObject) {

        var someData = inputArrayValues.stringValue
        let separators = NSCharacterSet(charactersInString: " ,;:|")
        let parts = someData.componentsSeparatedByCharactersInSet(separators)
        if (someData.characters.count > 0) {
            someData = "0"
        }

        let intArray = parts.map{Double($0)!} // on that line crush occurs

        let minArray = intArray.minElement()
        let maxArray = intArray.maxElement()

        let minString = String(minArray)
        let maxString = String(maxArray)

        minLabel.stringValue = "The minimal value is \(minString)!"
        maxLabel.stringValue = "The maximal value is \(maxString)!"

    }

So, how to check for nil and prevent app from crush??