fix(core): allow null / undefined values in query results (#35796)

Before this change ngIvy implementation of queries would throw upon
encountering null / undefined query result collected from an embedded
view. It turns out that we might have a provider that explicitly provides
a null / undefined value in a place of a token queried for.

This commit removes a check from the ngIvy query implementation that was
asserting on a query result to be defined.

Fixes #35673

PR Close #35796

packages/core/src/render3/query.ts

@@ -363,9 +363,7 @@ function collectQueryResults<T>(tView: TView, lView: LView, queryIndex: number,
     for (let i = 0; i < tQueryMatches.length; i += 2) {
       const tNodeIdx = tQueryMatches[i];
       if (tNodeIdx > 0) {
-        const viewResult = lViewResults[i / 2];
-        ngDevMode && assertDefined(viewResult, 'materialized query result should be defined');
-        result.push(viewResult as T);
+        result.push(lViewResults[i / 2] as T);
       } else {
         const childQueryIndex = tQueryMatches[i + 1];
 

packages/core/test/acceptance/query_spec.ts

@@ -1425,6 +1425,78 @@ describe('query logic', () => {
       expect(fixture.componentInstance.queryResults.last).toBeAnInstanceOf(WithMultiProvider);
     });
 
+    it('should allow undefined provider value in a [View/Content]Child queries', () => {
+      @Directive({selector: '[group]'})
+      class GroupDir {
+      }
+
+      @Directive(
+          {selector: '[undefinedGroup]', providers: [{provide: GroupDir, useValue: undefined}]})
+      class UndefinedGroup {
+      }
+
+      @Component({
+        template: `
+          <div group></div>
+          <ng-template [ngIf]="true">
+            <div undefinedGroup></div>
+          </ng-template>
+        `
+      })
+      class App {
+        @ViewChild(GroupDir) group !: GroupDir;
+      }
+
+      TestBed.configureTestingModule(
+          {declarations: [App, GroupDir, UndefinedGroup], imports: [CommonModule]});
+      const fixture = TestBed.createComponent(App);
+      fixture.detectChanges();
+
+      expect(fixture.componentInstance.group).toBeAnInstanceOf(GroupDir);
+    });
+
+    it('should allow null / undefined provider value in a [View/Content]Children queries', () => {
+      @Directive({selector: '[group]'})
+      class GroupDir {
+      }
+
+      @Directive({selector: '[nullGroup]', providers: [{provide: GroupDir, useValue: null}]})
+      class NullGroup {
+      }
+
+      @Directive(
+          {selector: '[undefinedGroup]', providers: [{provide: GroupDir, useValue: undefined}]})
+      class UndefinedGroup {
+      }
+
+      @Component({
+        template: `
+          <ng-template [ngIf]="true">
+            <div nullGroup></div>
+          </ng-template>
+          <div group></div>
+          <ng-template [ngIf]="true">
+            <div undefinedGroup></div>
+          </ng-template>
+        `
+      })
+      class App {
+        @ViewChildren(GroupDir) groups !: QueryList<GroupDir>;
+      }
+
+      TestBed.configureTestingModule(
+          {declarations: [App, GroupDir, NullGroup, UndefinedGroup], imports: [CommonModule]});
+      const fixture = TestBed.createComponent(App);
+      fixture.detectChanges();
+
+      const queryList = fixture.componentInstance.groups;
+      expect(queryList.length).toBe(3);
+
+      const groups = queryList.toArray();
+      expect(groups[0]).toBeNull();
+      expect(groups[1]).toBeAnInstanceOf(GroupDir);
+      expect(groups[2]).toBeUndefined();
+    });
 
   });