fixed doc env vars + mongo v2 migration

frontend/pweb/lib/pages/status/success.dart

@@ -36,8 +36,7 @@ class StatusPageSuccess extends StatelessWidget {
             style: Theme.of(context).textTheme.bodyMedium,
           ),
           const SizedBox(height: 20.0),
-          if (action != null)
-            action!,
+          ?action,
         ],
       ),
     ),

frontend/pweb/lib/services/posthog.dart

@@ -79,8 +79,8 @@ class PosthogService {
       'pageOpened',
       properties: {
         'page': page.name,
-        if (path != null) 'path': path,
-        if (uiSource != null) 'uiSource': uiSource,
+        'path': ?path,
+        'uiSource': ?uiSource,
       },
     );
   }