fix(core, android): fix a null issue when initializing fromResource() (#12404)

* fix(core, android): fix a null issue when initializing from ressources

* fix(core, android): fix a null issue when initializing from ressources

Author: Lyokone

packages/firebase_core/firebase_core/android/src/main/java/io/flutter/plugins/firebase/core/FlutterFirebaseCorePlugin.java

@@ -204,7 +204,9 @@ public void optionsFromResource(
           try {
             final FirebaseOptions options = FirebaseOptions.fromResource(applicationContext);
             if (options == null) {
-              taskCompletionSource.setResult(null);
+              taskCompletionSource.setException(
+                  new Exception(
+                      "Failed to load FirebaseOptions from resource. Check that you have defined values.xml correctly."));
               return;
             }
             taskCompletionSource.setResult(firebaseOptionsToMap(options));