fix(forms): properly handle special properties in FormGroup.get (#22249)

closes #17195

PR Close #22249

packages/forms/src/model.ts

@@ -44,7 +44,7 @@ function _find(control: AbstractControl, path: Array<string|number>| string, del
 
   return (<Array<string|number>>path).reduce((v: AbstractControl, name) => {
     if (v instanceof FormGroup) {
-      return v.controls[name] || null;
+      return v.controls.hasOwnProperty(name as string) ? v.controls[name] : null;
     }
 
     if (v instanceof FormArray) {

packages/forms/test/form_group_spec.ts

@@ -629,6 +629,18 @@ import {of } from 'rxjs';
       });
     });
 
+    describe('retrieve', () => {
+      let group: FormGroup;
+
+      beforeEach(() => {
+        group = new FormGroup({
+          'required': new FormControl('requiredValue'),
+        });
+      });
+
+      it('should not get inherited properties',
+         () => { expect(group.get('constructor')).toBe(null); });
+    });
 
     describe('statusChanges', () => {
       let control: FormControl;