Null Exception for Model Updates (#31)

* initial commit for Null Exception for Model Updates

* add null fix

src/field.ts

@@ -180,7 +180,7 @@ export class FieldImplementation<T, Model>
   };
 
   updateOriginalValue(value: Partial<T>): void {
-    if (typeof value === 'object') {
+    if (value && typeof value === 'object') {
       this.#originalValue = { ...this.#originalValue, ...value };
       Object.keys(value).forEach((key) => {
         const field = this.fields[key];

src/form.spec.ts

@@ -535,6 +535,12 @@ describe(Form, () => {
       expect(form.fields.name.value).toEqual('Jorge');
     });
 
+    it('allows updating the underlying model even with null values', async () => {
+      const form = createForm({ value: { name: undefined } });
+      form.updateOriginalModel({ name: null }); // null counts as an object, check that it doesn't break
+      expect(form.model.name).toBeNull();
+    });
+
     it('does not change the dirty status when changing the underlying model', async () => {
       const form = createForm({ value: { name: 'Klaus' } });
       form.fields.name.onChange('Claudia');