md-date-locale-provider: Error returning falsy value from parseDate

Returning eg. null from parseDate function on md-date-locale-provider causes a crash when manually setting a date value of an md-datepicker:

TypeError: Cannot read property 'setHours' of null
    at Object.g [as setDateTimeToMidnight] (angular-material.min.js:9)
    at o.handleInputEvent (angular-material.min.js:9)
    at angular-material.min.js:7
    at angular.min.js:145
    at e (angular.min.js:42)
    at angular.min.js:45

Expected behaviour:
Setting null marks the md-datepicker input as invalid.

Workaround:
Return new Date(NaN)