fix: add underlyingException to FirebaseJsonException when projectId or appId are missing (#364)

Author: Leedwon

packages/flutterfire_cli/lib/src/commands/upload_symbols.dart

@@ -313,7 +313,10 @@ class UploadCrashlyticsSymbols extends FlutterFireCommand {
     }
 
     if (projectId == null || appId == null) {
-      throw FirebaseJsonException();
+      final underlyingException =
+          projectId == null ? 'projectId is missing.' : 'appId is missing.';
+
+      throw FirebaseJsonException(underlyingException: underlyingException);
     }
 
     return ConfigurationResults(

packages/flutterfire_cli/lib/src/common/strings.dart

@@ -136,7 +136,7 @@ class FirebaseJsonException implements FlutterFireException {
   final String? underlyingException;
   @override
   String toString() {
-    return 'FirebaseJsonException: Please run "flutterfire configure" to update the `firebase.json` at the root of your Flutter project with correct values. ${underlyingException != null ? '' : underlyingException}';
+    return 'FirebaseJsonException: Please run "flutterfire configure" to update the `firebase.json` at the root of your Flutter project with correct values. ${underlyingException ?? ''}';
   }
 }