fix(microservices/nats): Check replyTo channel existence

packages/microservices/server/server-nats.ts

@@ -123,11 +123,17 @@ export class ServerNats extends Server implements CustomTransportStrategy {
   }
 
   public getPublisher(publisher: Client, replyTo: string, id: string) {
-    return (response: any) => {
-      Object.assign(response, { id });
-      const outgoingResponse = this.serializer.serialize(response);
-      return publisher.publish(replyTo, outgoingResponse);
-    };
+    if (replyTo) {
+      return (response: any) => {
+        Object.assign(response, { id });
+        const outgoingResponse = this.serializer.serialize(response);
+        return publisher.publish(replyTo, outgoingResponse);
+      };
+    }
+
+    // request doesn't need reply, return noop function
+    // eslint-disable-next-line @typescript-eslint/no-empty-function
+    return () => {};
   }
 
   public handleError(stream: any) {

packages/microservices/test/server/server-nats.spec.ts

@@ -142,23 +142,31 @@ describe('ServerNats', () => {
     let pub, publisher;
 
     const id = '1';
-    const replyTo = 'test';
-
     beforeEach(() => {
       publisherSpy = sinon.spy();
       pub = {
         publish: publisherSpy,
       };
-      publisher = server.getPublisher(pub, replyTo, id);
     });
     it(`should return function`, () => {
       expect(typeof server.getPublisher(null, null, id)).to.be.eql('function');
     });
-    it(`should call "publish" with expected arguments`, () => {
+    it(`should call "publish" when replyTo provided`, () => {
+      const replyTo = 'test';
+      publisher = server.getPublisher(pub, replyTo, id);
+
       const respond = 'test';
       publisher({ respond, id });
       expect(publisherSpy.calledWith(replyTo, { respond, id })).to.be.true;
     });
+    it(`should not call "publish" when replyTo NOT provided`, () => {
+      const replyTo = undefined;
+      publisher = server.getPublisher(pub, replyTo, id);
+
+      const respond = 'test';
+      publisher({ respond, id });
+      expect(publisherSpy.notCalled);
+    });
   });
   describe('handleEvent', () => {
     const channel = 'test';