fix(router): throw an error when navigate to null/undefined path

Closes #10560

Fixes #13384

modules/@angular/router/test/integration.spec.ts

@@ -536,6 +536,17 @@ describe('Integration', () => {
        expect(cmp.recordedParams).toEqual([{name: '1'}]);
      })));
 
+  it('should throw an error when one of the commands is null/undefined',
+     fakeAsync(inject([Router], (router: Router) => {
+       createRoot(router, RootCmp);
+
+       router.resetConfig([{path: 'query', component: EmptyQueryParamsCmp}]);
+
+       expect(() => router.navigate([
+         undefined, 'query'
+       ])).toThrowError(`The requested path contains undefined segment at index 0`);
+     })));
+
   it('should push params only when they change', fakeAsync(inject([Router], (router: Router) => {
        const fixture = createRoot(router, RootCmp);