fix exception on empty credentials

app/controllers/sessions_controller.rb

@@ -82,7 +82,7 @@ class SessionsController < ApplicationController
       return login_failed
     end
 
-    if login_user_id.empty? || params[:password].empty?
+    if !login_user_id.present? || !params[:password].present?
       return new_login_session
     end