phase3: nullfix.py batch script — bang/late/param-nullable

Automated null-safety fixes driven by dart analyze (no corruption):
- unchecked_use_of_nullable_value: insert '!' on receiver (property/method/[]/op)
- not_initialized field/var: mark 'late'
- missing_default_value_for_parameter: nullable param
Errors: 2374(peak) -> 907

lib/widgets/desktop/desktop_coupons.dart

@@ -27,7 +27,7 @@ class DesktopCoupons extends StatefulWidget {
 }
 
 class DesktopCouponsState extends State<DesktopCoupons> {
-  List<Coupon> coupons;
+  late List<Coupon> coupons;
 
   double sideSpace = 0;
   double mainSpace = 1200;
@@ -120,7 +120,7 @@ class DesktopCouponsState extends State<DesktopCoupons> {
                 Container(
                   padding: EdgeInsets.only(right: 5.0),
                   child: coupon.store != null ?
-                  Util.showImage('${coupon.store.picUrl}',
+                  Util.showImage('${coupon.store!.picUrl}',
                     fit: BoxFit.fill,
                     width: 40.0,
                   ) :
@@ -137,7 +137,7 @@ class DesktopCouponsState extends State<DesktopCoupons> {
                     crossAxisAlignment: CrossAxisAlignment.start,
                     children: <Widget>[
                       Text(
-                        coupon.store != null ? coupon.store.name : S.of(context).general_coupon,
+                        coupon.store != null ? coupon.store!.name : S.of(context).general_coupon,
                         style: TextStyle(
                           fontSize: 20.0,
                           fontWeight: FontWeight.bold,
@@ -221,7 +221,7 @@ class DesktopCouponsState extends State<DesktopCoupons> {
         ),
         Container(
           child: Text(
-            coupon.minAmount > 0 ?
+            coupon.minAmount! > 0 ?
             S.of(context).available_for_order_over_token(coupon.minAmount) :
             S.of(context).no_restriction,
             style: TextStyle(
@@ -259,7 +259,7 @@ class DesktopCouponsState extends State<DesktopCoupons> {
         children: <Widget>[
           Container(
             child: Text(
-              coupon.expirationDate == null || coupon.expirationDate.length == 0 ?
+              coupon.expirationDate == null || coupon.expirationDate!.length == 0 ?
                   S.of(context).no_expiration :
                   S.of(context).expiration_date_token(coupon.expirationDate),
               style: TextStyle(
@@ -284,7 +284,7 @@ class DesktopCouponsState extends State<DesktopCoupons> {
               ),
               onPressed: () {
                 if (coupon.store != null) {
-                  Routes.router.navigateTo(context, '/shop/${coupon.store.id}/na/na/na');
+                  Routes.router.navigateTo(context, '/shop/${coupon.store!.id}/na/na/na');
                 } else {
                   Routes.router.navigateTo(context, '/businesses');
                 }