Layout '2' without defaults causes React warnings.

This UI spec in model.js:
```
        {
          id: 'restart_write',
          type: 'string',
          size: 2,
          layout: '2',
          //default: ['', ''],
          label: 'Restart Write',
        },
```
without the 'default' provided (as shown), causes React 16 to warn about 'null' provided as a value for inputs, and converting controlled to uncontrolled components.