The sixmodel VTABLE find_method calls the find_method
in the containers STABLE which will throw instead of
returning NULL if it can't find the method.
Anything which is calling the VTABLE find_method is not
going to be expecting an exception so catch any exception
and return NULL.
Hmm, it looks like this isn't good enough as an exception handler. I'm geting segfault's when I've intercepted an exception
and returned NULL to another C routine which sees the NULL and throw's it's own exception.