Of course null causes no problem; that just gets mapped to undef. true and false get mapped to bless $Class, \$bool. It appears that one of your systems is blessing into a class that is not special-cased in the other direction. Perhaps this is because the TO_JSON() method is not being defined. But, no, I have no idea why it gets defined on one server and not on the other. Surely, there are differences between the servers, despite you thinking that there are none.