Don't auth if password is empty as REDIS doesn't support it

[marcosnils]

Fixes #1808

[sazzad16]

@marcosnils
IMHO, throwing exception from constructor would be better approach for this case. Completely ignoring values sent by user doesn't seem to be a good idea.

PS: #1808 is closed.

[dnatic09]

My team has run into this problem before. I inherited a library with default configuration containing a password. I was unable to blank out the password by overriding the configuration. Instead of changing my configuration, I had to reconfigure my Redis servers. This would alleviate that issue.

[marcosnils]

Just double checked and Redis actually allows you to start a server with an empty password and authenticate against it.

redis-server - <<< "requirepass \"\""
redis-cli
127.0.0.1:6379> auth ""
OK
127.0.0.1:6379>