TIL, 2017-02-17

Don’t use backticks when committing. gc "Use 'hello' will try to execute hello command. (if the ‘ was a backtick, it’s hard to parse in jekyll).”
API design, if you are going to add contacts with a bunch of emails or something, better to just fail all rather than pass the valid ones and report the fails, that way you can’t add twice. Front-end will get errors one by one.
which rake to figure out where the version of rake is coming from, at least you will prevent the using bundle exec will help error message. Or better yet just use bundle exec when in the context of a rails project to ensure that the Gemfile gem is the one being used rather than the system one.
This will work: User.where(User.arel_table[:email].not_eq(nil)), better to read and you will clarify that the email field is coming from the users table (just in case you join this at some point).