List<Predicate> predicates = new ArrayList<Predicate>();

//Adding predicates in case of parameter not being null
if (param1 != null) {
    predicates.add(
            qb.equal(customer.get("someAttribute"), param1));
}
if (paramNull != null) {
    predicates.add(
            qb.equal(customer.get("someOtherAttribute"), paramNull));
}
//query itself
cq.select(customer)
        .where(predicates.toArray(new Predicate[]{}));