public void visitMembers(ObjectVisitor visitor) {
        visitor.visit("classId", getClassId());
    }
This function needs to be implemented in such a way that it visits all its members. This is done by invoking the
{@link com.yahoo.vespa.objects.ObjectVisitor#visit(String, Object)} on the visitor argument for all members.

@param visitor The visitor that is to access the member data.
vespajlib/src/main/java/com/yahoo/vespa/objects/Identifiable.java