Resolve gemini review comments and add a unit test

Author: yvonnep165

src/messaging/messaging-errors-internal.ts

@@ -33,9 +33,10 @@ export function createFirebaseError(err: RequestResponseError): FirebaseMessagin
     const errorMessage = getErrorMessage(json);
     if (errorCode === 'UNREGISTERED' || errorCode === 'NOT_FOUND') {
       let requestData = err.response.config && err.response.config.data;
-      if (typeof requestData === 'string') {
+      if (requestData && (typeof requestData === 'string' || Buffer.isBuffer(requestData))) {
         try {
-          requestData = JSON.parse(requestData);
+          const strData = typeof requestData === 'string' ? requestData : requestData.toString('utf-8');
+          requestData = JSON.parse(strData);
         } catch (e) {
           // Ignore parsing errors.
         }

src/messaging/messaging.ts

@@ -324,17 +324,18 @@ export class Messaging {
 
     const { tokens, fids, ...baseMessage } = copy;
 
-    const tokenList: string[] = tokens || [];
-    const fidList: string[] = fids || [];
-
-    if ('tokens' in copy && !validator.isArray(copy.tokens)) {
+    if (tokens !== undefined && !validator.isArray(tokens)) {
       throw new FirebaseMessagingError(
         MessagingClientErrorCode.INVALID_ARGUMENT, 'tokens must be a valid array');
     }
-    if ('fids' in copy && !validator.isArray(copy.fids)) {
+    if (fids !== undefined && !validator.isArray(fids)) {
       throw new FirebaseMessagingError(
         MessagingClientErrorCode.INVALID_ARGUMENT, 'fids must be a valid array');
     }
+
+    const tokenList: string[] = tokens || [];
+    const fidList: string[] = fids || [];
+
     if (tokenList.length === 0 && fidList.length === 0) {
       throw new FirebaseMessagingError(
         MessagingClientErrorCode.INVALID_ARGUMENT, 'Either tokens or fids must be a non-empty array');

test/unit/messaging/messaging.spec.ts

@@ -1224,6 +1224,18 @@ describe('Messaging', () => {
         });
     });
 
+    it('should handle explicitly undefined tokens or fids gracefully without throwing', () => {
+      stub = sinon.stub(messaging, 'sendEach').resolves(mockResponse);
+      return messaging.sendEachForMulticast({ fids: ['f1'], tokens: undefined } as any)
+        .then((response: BatchResponse) => {
+          expect(response).to.deep.equal(mockResponse);
+          expect(stub).to.have.been.calledOnce;
+          const messages: Message[] = stub!.args[0][0];
+          expect(messages.length).to.equal(1);
+          expect((messages[0] as FidMessage).fid).to.equal('f1');
+        });
+    });
+
     it('should create multiple messages using mixed tokens and fids', () => {
       stub = sinon.stub(messaging, 'sendEach').resolves(mockResponse);
       const tokens = ['t1', 't2'];