Catch null key (caused by wrong cert filename) before jdk catches it and throws an unhelpful exception instead

[alechenninger]

Had this happen to me, putting this here so we have a better error msg in the future. If your cert's filename does not match its alias, you'll get a cryptic exception about a keystore not allowing non-private keys, when really it is because the key is null, which is because there was no key associated with the alias, which is because the alias was wrong, which is because the filename was wrong. Wowsa!

[alechenninger]

This happens at line ~148 on SslSocketFactories

[jblashka]

I would suggest having the cert alias be a configuration property instead of assuming the cert alias is the keystore file base name. We also just ran into this.

[derek63]

The certAlias used to be separately configurable but it was removed in #20. We could always add it back...