TimePicker return null in CustomDateTimePicker components

I was try CustomDateTimePicker components defined here:
https://vaadin.com/components/vaadin-custom-field/java-examples

In generateModelValue() method timePicker.getValue()
always return null.

I’m set binder and required validator for this component:

	CustomDateTimePicker begin = new CustomDateTimePicker("Begin");
	binder.forField(begin).asRequired("Required").bind(NE::getBegin, NE::setBegin);
	l.addFormItem(begin, "Begin");

when I set values in browser for date and time I got validation error “Required”.
TimePicker return null.

I notice that if I first select the time then the date then it works well. But the reverse does not work.