Checking MIMe type 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, i think that finding the MIME type is problem. 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 gettingImages(from array : NSMutableArray)
{

    // Performing progressView addition


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

        let imageManager : PHImageManager = PHImageManager()

        for index in 0...(array.count - 1)
        {

            var ID = imageManager.requestImageDataForAsset( array[index] as PHAsset, options: options, resultHandler: {

                data,string,orientation,object in

                if string == "public.png"
                {

                if let isIniCloud = object? [PHImageResultIsInCloudKey] as? NSNumber
                {

                    if isIniCloud == 0
                    {

                            if let MIME  = UTTypeCopyPreferredTagWithClass(string, kUTTagClassMIMEType)?.takeUnretainedValue()
                            {


                                if index == (array.count - 1)
                                {
                                    if MIME == "image/png"
                                    {                                        self.ImageArray.addObject(array[index])
                                    }
                                }
                                else
                                {
                                    if MIME == "image/png"
                                    {                                        self.ImageArray.addObject(array[index])
                                    }

                                }

                            } // End Of MIME type checking

                    } // Is in iCloud

                } // Is in iCloud
            }

            }) // Image Manager

        } // For loop
    }

Is there anybody knows why this happens, when i run it, it crashes.? Sometimes when i switch between iCloud Photo Stream ON/OFF, it works (very rare). Is this because of string value which am passing into UITypeCopy..Class.???