fix(core): error if DebugRenderer2.destroyNode is called twice in a row (#41565)

Fixes an error that will be thrown if  `DebugRenderer2.destroyNode` is called with a node that has already been destroyed. The error happened, because we had a non-null assertion, even though the value can be null.

Note that this fix applies only to ViewEngine, because Ivy doesn't provide the `DebugRenderer2`. I decided to resolve it, because it fix is straightforward and this error has been showing up in our logs for a long time now, making actual errors harder to find.

PR Close #41565

packages/core/src/view/services.ts

@@ -703,11 +703,15 @@ export class DebugRenderer2 implements Renderer2 {
   }
 
   destroyNode(node: any) {
-    const debugNode = getDebugNode(node)!;
-    removeDebugNodeFromIndex(debugNode);
-    if (debugNode instanceof DebugNode__PRE_R3__) {
-      debugNode.listeners.length = 0;
+    const debugNode = getDebugNode(node);
+
+    if (debugNode) {
+      removeDebugNodeFromIndex(debugNode);
+      if (debugNode instanceof DebugNode__PRE_R3__) {
+        debugNode.listeners.length = 0;
+      }
     }
+
     if (this.delegate.destroyNode) {
       this.delegate.destroyNode(node);
     }

packages/core/test/debug/debug_node_spec.ts

@@ -208,6 +208,7 @@ class TestApp {
   width = 200;
   color = 'red';
   isClosed = true;
+  constructor(public renderer: Renderer2) {}
 }
 
 @Component({selector: 'test-cmpt', template: ``})
@@ -618,6 +619,22 @@ class TestCmptWithPropInterpolation {
       expect(fixture.debugElement.query(By.css('.myclass'))).toBeTruthy();
     });
 
+    it('should not throw when calling DebugRenderer2.destroyNode twice in a row', () => {
+      const fixture = TestBed.createComponent(TestApp);
+      fixture.detectChanges();
+      const firstChild = fixture.debugElement.children[0];
+      const renderer = fixture.componentInstance.renderer;
+
+      expect(firstChild).toBeTruthy();
+      expect(() => {
+        // `destroyNode` needs to be null checked, because only ViewEngine provides a
+        // `DebugRenderer2` which has the behavior we're testing for. Ivy provides
+        // `BaseAnimationRenderer` which doesn't have the issue.
+        renderer.destroyNode?.(firstChild);
+        renderer.destroyNode?.(firstChild);
+      }).not.toThrow();
+    });
+
     describe('DebugElement.query with dynamically created descendant elements', () => {
       let fixture: ComponentFixture<{}>;
       beforeEach(() => {