MaterialDatePicker CONFIRM_BUTTON_TAG

I am writing a test for MaterialDatePicker. Trying to click the OK button currently.

This code here,

onView(withTagValue(equalTo(MaterialDatePicker.CONFIRM_BUTTON_TAG))).performClick();

Returns the error,

error: CONFIRM_BUTTON_TAG is not public in MaterialDatePicker; cannot be accessed from outside package

However in MaterialDatePickerTestUtils it seems to work? Link

UPDATE 1

onView(withId(R.id.confirm_button)).inRoot(isDialog()).perform(click());

Finds the button, but the error is that the view has no content.