Cannot read property of undefined error when returning to edit mode.

Steps:
1. Add the Form block to a Landing page.
2. Add the Email Simple form field.
3. Keep default values.
4. Submit.
5. Publish.
6. Click Edit.
Actual: "Cannot read property 'email' of undefined" error occurs. Fields tab is empty.
Expected: It's possible to return to edit mode w/o errors.

Remarks: Seems to occur only when field is set to required.