enums / oneoff do not allow no selection

[alastair-todd]

Describe the bug which template:

• [ ] MaterialDesignFrameworkModule — Material Design
• [X ] Bootstrap3FrameworkModule — Bootstrap 3
• [ ] Bootstrap4FrameworkModule — Bootstrap 4
• [ ] NoFrameworkModule — plain HTML
• [ ] Other (please specify below)

A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior:

1. from playground select "none" for the State in the address. Throws a validation error.

Expected behavior No validation error as it is not a required field