Association should respond to #empty? for compatibility with ActiveSupport's #blank? method

In our Rails project `user.comments.empty?` always returns `false`, because the association does not respond to `empty?`. See https://github.com/rails/rails/blob/2a371368c91789a4d689d6a84eb20b238c37678a/activesupport/lib/active_support/core_ext/object/blank.rb#L15