Update QRCodeModel

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: madebymozart

samples/camera/camerax/src/main/java/com/example/platform/camerax/mlkit/QrCodeViewModel.kt

@@ -38,7 +38,7 @@ class QrCodeViewModel(barcode: Barcode) {
     init {
         when (barcode.valueType) {
             Barcode.TYPE_URL -> {
-                qrContent = barcode.url!!.url!!
+                qrContent = barcode.url?.url ?: "Invalid URL"
                 qrCodeTouchCallback = { v: View, e: MotionEvent ->
                     if (e.action == MotionEvent.ACTION_DOWN && boundingRect.contains(
                             e.x.toInt(), e.y.toInt(),