Reducers can occasionally receive actions without a type

src/actions.spec.ts

@@ -0,0 +1,19 @@
+import { isNgrxFormsAction } from './actions';
+
+describe(isNgrxFormsAction.name, () => {
+  it('should return true if type is ngrx/forms/', () => {
+    expect(isNgrxFormsAction({ type: 'ngrx/forms/' })).toBe(true);
+  });
+
+  it('should return true if type startsWith ngrx/forms/', () => {
+    expect(isNgrxFormsAction({ type: 'ngrx/forms/test' })).toBe(true);
+  });
+
+  it('should return false if type does not have ngrx/forms/', () => {
+    expect(isNgrxFormsAction({ type: 'some-type' })).toBe(false);
+  });
+
+  it('should return false if type is missing', () => {
+    expect(isNgrxFormsAction({} as any)).toBe(false);
+  });
+});

src/actions.ts

@@ -334,5 +334,5 @@ export type Actions<TValue> =
   ;
 
 export function isNgrxFormsAction(action: Action) {
-  return action.type.startsWith('ngrx/forms/');
+  return !!action.type && action.type.startsWith('ngrx/forms/');
 }