Default value/button for button_group

i'm having the same issue as this topic:
https://support.metabox.io/topic/default-value-for-button_group-fields/

I have the following buttons:
*12345
* has the value of zero.

In the template the 12345 shows a star rating. But when it's zero then all the stars are grey (as it should) but to be 0 i need a 0 button.

When you enter 0:0 then the 0 button will not apear. thats why i use a *.

So what do i want, or that 0 can be a button AND that 0 is the default value
Or that i can say that the * is the default.