swift fatal error: unexpectedly found nil while unwrapping an Optional value(lldb)from email -in my code?

Question

这是我的代码，在这里找到了致命的 error.i 尝试解决这个问题，但它显示了很多次，并且显示了 EXC_BAD_INSTRUCTION(code=EXC_i386_INVOP,subcode= 0*0)

import UIKit
class VerifyProfileViewController: UIViewController,UITextFieldDelegate,FBLoginViewDelegate {
    var liveurl = demo_url

    @IBOutlet weak var f_name: UITextField!
    @IBOutlet weak var l_name: UITextField!
    @IBOutlet weak var email_id: UITextField!
    @IBOutlet weak var mobilenumber: UITextField!
    @IBOutlet weak var myLabel: UILabel!
    @IBOutlet weak var nextOutlet: UIButton!
    override func viewDidLoad() {
        super.viewDidLoad()

        // NSUserDefaults.standardUserDefaults().synchronize()
        var mobile_Number = mobilenumber.text
        var email_Address = email_id.text
        var first_name = f_name.text 
        var last_name = l_name.text
        var email1 = isValidEmail(email_Address)
        let email = NSUserDefaults.standardUserDefaults().objectForKey("fb_email") as NSString
        println("The email :\(email)")
        let first_name = NSUserDefaults.standardUserDefaults().objectForKey("fb_name") as NSString
        println("The firstname :\(first_name)")

        let last_name = NSUserDefaults.standardUserDefaults().objectForKey("fb_lname") as NSString
        println("The firstname :\(last_name)")
        //NSUserDefaults.standardUserDefaults().setObject(facebookid, forKey:"id")
        //let facebook_id = NSUserDefaults.standardUserDefaults().objectForKey("fb_id")! as NSString
        //println("The fbID :\(facebook_id)")
        email_id.text = email
        f_name.text = first_name
        l_name.text = last_name

Answer 1

NSUserDefaults.standardUserDefaults().setValue("abc@def.com", forKey: "fb_email")
if let email = NSUserDefaults.standardUserDefaults().stringForKey("fb_email") {
    println(email)
}