backend health checks and 204

[David Birdsong]

I couldn't find this anywhere, so apologies if it's already been hashed out.

Would it be possible for the backend health checks to be altered to
consider a 204 response from a backend as healthy?

In my case, nginx will only return a 200 if it sends something so I'll
use it's in memory gif, but I sure would like a 204 ;) to be a valid
'healty' response.