Is it possible to have an empty Date field?

[ychaker]

I have field called 'end_date' defined in my schema as:

property 'endDate', Date

and under my User model I have the current validation:

User.validatesFormatOf 'endDate', with: /dddd-dd-dd/, {message: 'should be in the following format: yyyy-mm-dd'}, allowBlank: true

Is there a way to allow for empty/blank values? The validation works but saving the user gives the following error: EndDate is invalid (Invalid Date)