According to the redis-py docs, zrank will return the 0 based index for
the value in the sorted set. So the logic here wasn't right to begin
with (It just means that a value at the 0-th position would never show
up as cached). Need to compare against None to know if the value
exists in the cache.
https://redis-py.readthedocs.io/en/latest/#redis.StrictRedis.zrankFixes#25590
90b1d780eb