enhancement(@nestjs/microservices) use isString helper instead

Author: Kamil

packages/microservices/server/server.ts

@@ -1,13 +1,7 @@
 import { Logger } from '@nestjs/common/services/logger.service';
 import { loadPackage } from '@nestjs/common/utils/load-package.util';
-import { isFunction } from '@nestjs/common/utils/shared.utils';
-import {
-  EMPTY as empty,
-  Observable,
-  Subscription,
-  from as fromPromise,
-  of,
-} from 'rxjs';
+import { isFunction, isString } from '@nestjs/common/utils/shared.utils';
+import { EMPTY as empty, from as fromPromise, Observable, of, Subscription } from 'rxjs';
 import { catchError, finalize } from 'rxjs/operators';
 import { MessageHandlers } from '../interfaces/message-handlers.interface';
 import { MicroserviceOptions, WritePacket } from './../interfaces';
@@ -16,6 +10,14 @@ export abstract class Server {
   protected readonly messageHandlers: MessageHandlers = {};
   protected readonly logger = new Logger(Server.name);
 
+  public addHandler(
+    pattern: any,
+    callback: (data) => Promise<Observable<any>>,
+  ) {
+    const key = isString(pattern) ? pattern : JSON.stringify(pattern);
+    this.messageHandlers[key] = callback;
+  }
+
   public getHandlers(): MessageHandlers {
     return this.messageHandlers;
   }
@@ -26,14 +28,6 @@ export abstract class Server {
     return this.messageHandlers[pattern] ? this.messageHandlers[pattern] : null;
   }
 
-  public addHandler(
-    pattern: any,
-    callback: (data) => Promise<Observable<any>>,
-  ) {
-    const key = typeof pattern === 'string' ? pattern : JSON.stringify(pattern);
-    this.messageHandlers[key] = callback;
-  }
-
   public send(
     stream$: Observable<any>,
     respond: (data: WritePacket) => void,