I have had 1 WC northern, a gorgeous black male. It was given to me because it would not eat. Wouldn't eat rodents anyway. I tried just to be sure - correct, it wouldn't eat rodents, live, dead, rat, mouse, hamster, nuh-uh. The snake's owner (a dealer and a friend) was too busy to put much time into the animal. I think he'd gotten it as part of an entire collection he bought.
The animal was dangerously thin, so I tube-fed it several hopper mice once. Luckily however, I discovered the snake fancied frozen/thawed chicks and quail (which I'd purchased for another fussy feeder). After I got weight back on it, this timber switched over to rodents pretty easily (frozen/thawed adult mice).
I then gave it back to the former owner, who promptly turned it over to another friend here in FL with a small collection of black timbers. I understand it still feeds great. Hopefully it'll pass on its pretty genes...
I'm not even going to address all the basic environmental needs - I'll just assume those are already being well-met, and this is an honest case of "snake just won't eat", not inept husbandry. The 1 timber I had was a little nervous, much more so than the "canes" I'm much more familiar with. He did well with security (is "yours" on display?).
Best of luck,
Jimi