Blank date required

I am looking to see if this control can be used when a date can be entered or not depending on needs. In my case the user records the last date an event occurred, but it is possible that the event has not occurred before and should be blank. Currently the angularJS Model is not updated by clearing an input box:

<input required="false"  format="yyyy-MM-dd" type="text" min-view="date" date-time data-ng-model="last_action">{{last_action}}

Is there a way to allow the clearing of the input box to update the model?

[mdedetrich]

+1

Ideally the plugin should detect if the field is optional, and if it is, then allow for blank/nullable fields

[spirant]

On further review it also appears that the date-picker is triggering an automated validation which prevents an input being left blank when saving a form. Any thoughts on how to allow this would be much appreciated.