Validate datepicker without click

How can I validate datepicker using keyboard/tab key,
validation work when I click the picker, return value always null using keyboard
https://snippet.webix.com/0pyi6dpy

Please note that partial validation if possible only if the control has validate property. Otherwise, it is possible to validate only the entire form.

Please, check the following snippet: https://snippet.webix.com/6f6fj7xn