diff --git a/src/app/pages/home/home-page.component.ts b/src/app/pages/home/home-page.component.ts
index a4fc8f2..daefa1e 100644
--- a/src/app/pages/home/home-page.component.ts
+++ b/src/app/pages/home/home-page.component.ts
@@ -46,7 +46,7 @@ export class HomePageComponent implements OnInit, OnDestroy {
   private discoveryContainerWidth: number;
   private discoveryContainerHeight: number;
   private discoveryStartDate: Date;
-  private discoveryRequestID: string;
+  private discoveryRequestID: string | null;
   private readonly maxScale: number;
   private readonly minScale: number;
 
@@ -70,7 +70,9 @@ export class HomePageComponent implements OnInit, OnDestroy {
 
   @HostListener('window:beforeunload', ['$event'])
   onBeforeUnload(event) {
-    this.probeService.send('DiscoveryService.DiscoverStop', requesterID, this.discoveryRequestID);
+    if (null !== this.discoveryRequestID) {
+      this.probeService.send('DiscoveryService.DiscoverStop', requesterID, this.discoveryRequestID);
+    }
     // event.returnValue = true;
   }
 
@@ -88,6 +90,8 @@ export class HomePageComponent implements OnInit, OnDestroy {
     this.hosts = [];
     this.ports = [];
 
+    this.discoveryRequestID = null;
+
     this.maxScale = 1;
     this.minScale = 0.7;
   }
@@ -552,7 +556,7 @@ export class HomePageComponent implements OnInit, OnDestroy {
   @RPCSubscriber({ method: 'DiscoveryService.QueueingTimeout' })
   public DiscoveryQueueingTimeout(queueingTimeoutDate: Date) {
     console.log('DiscoveryQueueingTimeout', queueingTimeoutDate);
-    this.discoveryRequestID = '';
+    this.discoveryRequestID = null;
   }
 
   /**
@@ -571,7 +575,7 @@ export class HomePageComponent implements OnInit, OnDestroy {
   public DiscoveryStop(stopDate: Date) {
     console.log('DiscoveryStop', stopDate);
 
-    this.discoveryRequestID = '';
+    this.discoveryRequestID = null;
 
     const _millisecond = Math.abs(stopDate.getTime() - this.discoveryStartDate.getTime());