Datepicker Default Value Should Be NULL.

The default value of the date picker should be NULL instead of the current date. Otherwise, there is the potential for the user to submit arbitrary values.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| Refs tickets  | -
| License       | MIT
| Doc PR        | -