fetch executes fallback if cached value is nil about cachex

[whitfin]

If you want to PR this somewhere in docs, go ahead. The use of nil generally represents no value, so putting nil into the cache is a weird pattern in the first place; the only case I can think of is checking presence, in which case using something like true is probably better.

It's pretty much just a side effect from ETS itself, it's not something done in this lib. If an empty key comes back from ETS, it's nil. There's no other way to communicate a cache miss other than nil.

[whitfin]

I'm going to close this out, because this is pretty much ETS behaviour. If someone places nil in ETS, it's pretty much the same as nothing being there. There's a chance we can figure out a good way to work around it if more people need it, but I would suggest using something other than nil!