style: if ! changed by unless

- if ! changed by unless as it is more readable
- !object.blank? is equivalent to object.present?, also more readable

app/controllers/application_controller.rb

@@ -47,7 +47,7 @@ class ApplicationController < ActionController::Base
   rescue_from CanCan::AccessDenied do |exception|
     Rails.logger.debug "Access denied on #{exception.action} #{exception.subject.inspect}"
     message = exception.message
-    message << ' Maybe you need to sign in?' if !current_user
+    message << ' Maybe you need to sign in?' unless current_user
     redirect_to root_path, alert: message
   end