Swift 2.2检查字符串或int为nil

Question

我刚刚为自己学习了新语言 - 很快，现在我遇到了空值的问题。我编写一个简单的应用程序来搜索数组的最小值和最大值。但是如果在app中输入空值 - crush会发生错误： 致命错误：在解包可选值（lldb）时意外发现nil

我尝试在nil和isEmpty上实现一些检查，但app仍在破碎。

以下是代码：

 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)!"

    }

那么，如何检查nil并防止app崩溃？