About RPC, leaving it blank doesn't it simply setup RPC without user/pass? Just asking, I don't really know for sure, haven't looked at the code
Without RPC settings in conf-file I had an authorization failure in Sentinel.
Then I add 'rpcuser' and 'rpcpassword' to desire.conf this failure disappeared.
desire-cli works fine in both scenarios: with or without 'rpcuser' and 'rpcpassword' in desire.conf