check null safety

lib/pages/contact/contact_page.dart

@@ -21,7 +21,8 @@ class ContactPage extends StatefulWidget {
 class _ContactPageState extends State<ContactPage> {
   @override
   Widget build(BuildContext context) {
-    Setting setting = Provider.of<MainModel>(context).setting;
+    Setting? setting = Provider.of<MainModel>(context).setting;
+    if (setting == null) return Container();
     bool isEditable = context.select((MainModel m) => m.contactEditable());
 
     return Scaffold(
@@ -61,14 +62,14 @@ class _ContactPageState extends State<ContactPage> {
         children: [
           itemTitle(context, "contact.callus"),
           contactItem(context, setting.usaContactNumber, CupertinoIcons.phone,
-              onTap: () => _call(setting.usaContactNumber),
+              onTap: () => _call(setting.usaContactNumber ?? ""),
               labelKey: "contact.usa.phone"),
           contactItem(
             context,
             setting.mmContactNumber,
             CupertinoIcons.phone,
             onTap: () => _call(
-              setting.mmContactNumber,
+              setting.mmContactNumber ?? "",
             ),
             labelKey: "contact.mm.phone",
           ),
@@ -90,7 +91,7 @@ class _ContactPageState extends State<ContactPage> {
             context,
             setting.emailAddress,
             CupertinoIcons.mail,
-            onTap: () => _email(setting.emailAddress),
+            onTap: () => _email(setting.emailAddress ?? ""),
             labelKey: "contact.fcs.email",
           ),
           itemTitle(context, "contact.visitus"),
@@ -98,7 +99,7 @@ class _ContactPageState extends State<ContactPage> {
             context,
             setting.facebookLink,
             FontAwesomeIcons.facebook,
-            onTap: () => _opencontactItem(setting.facebookLink),
+            onTap: () => _opencontactItem(setting.facebookLink ?? ""),
             labelKey: "contact.facebook",
           ),
         ],