Set cardinality in empty BoundSetDomain() constructor

I was creating BoundSetDomains by using code like this:

domain = new BoundSetDomain();
for (int i : someListIHave()) {
	domain = domain.union(i);
}

Sometimes, however, this list is empty, which leads to
an empty BoundSetDomain, which does not have a cardinality.

Later one, when I called search.labeling(), I got a
NullPointerException in BoundSetDomain.inCardinality:1265.
This line checks for
  min <= cardinality.min()
which raises a NullPointerException as cardinality is null for
my BoundSetDomain.

I tried to create a very simple test case to show the issue,
but I was not able in the short amount of time I have.

It seems like the error only occurs in my complex set of constraints
I have.

However, I think it is reasonable to set the cardinality
to 0 for an empty SetDomain, isn't it?