swift - Trying to DateFormatting Optional String -

currently i'm getting invoice data rails api.

func get(path: string) {     let url = nsurl(string: path)     let session = nsurlsession.sharedsession()     let task = session.datataskwithurl(url!, completionhandler: {data, response, error -> void in         if(error != nil) {             print(error!.localizeddescription)         }         {             let results = try nsjsonserialization.jsonobjectwithdata(data!, options: nsjsonreadingoptions.mutableleaves)             self.delegate.didreceiveapiresults(results as! nsarray)         } catch {             print("error")         }     })      task!.resume() } 

then pass array results delegate in invoicescontroller:

func didreceiveapiresults(results: nsarray) {     let dateformatter = nsdateformatter()     dateformatter.dateformat = "yyyy-mm-dd't'hh:mm:ss.sssz"     dispatch_async(dispatch_get_main_queue(), {         invoice in results {             // create individual item             invoice.createinmanagedobjectcontext(self.managedobjectcontext,                 invoicestatus: string(invoice["status"]),                 invoiceprice: nsdecimalnumber(string: string(invoice["price"])),                 invoicedate: dateformatter.datefromstring("2015-06-22t17:57:21.313z")!,                 invoiceduedate: string(invoice["invoice_date"])              )         }     }) } 

but can't convert invoice["invoice_date"] optional valid date, returns nil.

i've tried things in playground , there works optional value:

let dateformatter = nsdateformatter() dateformatter.dateformat = "yyyy-mm-dd't'hh:mm:ss.sssz"  var datestring:string? = "2015-06-22t17:57:21.313z"  dateformatter.datefromstring(datestring!) 

by using:

invoicedate: dateformatter.datefromstring(string(invoice["invoice_date"]))! 

i'm getting error:

fatal error: unexpectedly found nil while unwrapping optional value (lldb)  

someone suggestions? i'm using swift 2 on ios 9 platform.

question answered in comments, thought i'd put here:

there problem in cast, , using

invoice["invoice_date"] as! string 

solved it.