Prevent nginx caching empty pages?

[John Moore]

Hi,

I'm trying to diagnose a problem we have on a rather complex system with 
an nginx acting as a remote proxy server, where what appears to be a 
completely empty response is being returned, seemingly from the nginx 
cache. It's early days yet in my troubleshooting, so this may not 
actually be the problem, but just in case, I have two questions:

1. Is this actually possible? Will nginx actually cache an empty 
response? (I am not sure how an empty response could actually come from 
the back end without being marked with some kind of error response 
header, which would presumably prevent any caching, but that's a 
different issue).

2. If it is possible, is there any way to prevent it from happening? 
E.g., setting some kind of minimal cachable size for the cache? This is 
using the now rather ancient version 0.7.65, I'm afraid.

John M