ITCR — Question on unions default member

In the section 6.14.2 on union mapping, it says :
"If there is a default case specified, the union is initialized to this default case. In case the union has an implicit default member it is initialized to that case. In all other cases it is initialized as empty."

I don't get the meaning of "empty" and it doesn't seem to be defined. For example, if we have a union with a boolean discriminator which defines the two cases true and false, what happens if we read one of the fields or if we call _d (with or without parameter)? Should they all throw BAD_PARAM?

Improve description of union

After some prototyping and looking at the normal C+11 unions we propose to initialize the union in all other cases to the first discriminant in IDL, this is matching C+11 unions