Checking property of images crashing in swift

I used this function to scan all photos from the Camera Album in iPhone/ iPad. I don't know why, for me it was crashing all the time. I really don't have any idea about where it is crashing in this function, . Sometimes it worked fine, when I changed iCloud Photo Stream to ON/OFF in Settings in iPhone/IPad. I have no idea why this happens.

This is the function which I wrote. I am passing array of PHAssets into this function.

 func gettingSize(from array : NSMutableArray)
    {
        func enumerateAllImages(imageArray : NSMutableArray, completion : ((ArrayPassed : NSMutableArray) -> Void)?)
        {

            // Performing progressView addition

            var TempArray : NSMutableArray = NSMutableArray()

            var options : PHImageRequestOptions = PHImageRequestOptions()
            options.synchronous = true
            options.networkAccessAllowed = false // to skip download image from iCloud

            let imageManager : PHImageManager = PHImageManager()

            for index in 0...(imageArray.count - 1)
            {
                var ID = imageManager.requestImageDataForAsset( imageArray[index] as PHAsset, options: options, resultHandler:
                    {
                        data,stringValue,orientation,object in

                        var value : NSString = stringValue

                        if (value as NSString).containsString(".png")
                        {
                            if let isIniCloud = object as NSDictionary?
                            {
                                var isIniCloudDICT : NSDictionary = isIniCloud

                                if let integerCloudValue = isIniCloudDICT.valueForKeyPath(PHImageResultIsInCloudKey) as? Int
                                {

                                    if integerCloudValue == 0
                                    {
                                        if index == (imageArray.count - 1)
                                        {
                                            self.tempImageSize = self.tempImageSize + data.length
                                            TempArray.addObject(imageArray[index])
                                            self.increasingTheValue()
                                            completion!(ArrayPassed: TempArray)
                                        }
                                        else
                                        {
                                            self.tempImageSize = self.tempImageSize + data.length
                                            TempArray.addObject(imageArray[index])
                                        }

                                    } // Checking condition for integerValueCloud
                                    else
                                    {
                                        if index == (imageArray.count - 1)
                                        {
                                            completion!(ArrayPassed: TempArray)
                                        }
                                    }

                                } // Is in iCloud Optional checking
                                else
                                {
                                    if index == (imageArray.count - 1)
                                    {
                                        completion!(ArrayPassed: TempArray)
                                    }
                                }

                            } // Is in iCloud NSDictionary optional checking
                            else
                            {
                                if index == (imageArray.count - 1)
                                {
                                    completion!(ArrayPassed: TempArray)
                                }
                            }
                        }
                        else
                        {
                            if index == (imageArray.count - 1)
                            {
                                completion!(ArrayPassed: TempArray)
                            }
                        }
                }) // Image Manager
            } // For loop
        } // Nested Function

        enumerateAllImages( array, { ArrayPassed in

            if ArrayPassed.count == 0
            {
                dispatch_async(dispatch_get_main_queue(), {

                    self.progressView.progress = 0
                    self.tempProgress = 0
                    self.increasingTheValue()
                })
            }
            else
            {
                self.Array = ArrayPassed
            }
        })
    }

Does anybody knows why this happens, when I run it, it crashes? Crahes on this line

 var value : NSString = stringValue

Multiple times, no idea why this happens.?