rails 4 undesired double pop-up

Question

In my rails 4 application session expire time set to 10 minutes for user login.

After that user clicks on any link the default flash message is comes up like Your session is expired. Please sign in again to continue.

This is fine, but below this another flash message is coming like "true" . I don't know from where it is coming from, how can I solve this?

---

Application Controller

def layout_by_resource 
  if devise_controller? && resource_name == :operator && (action_name == 'sign_in' and params[:login_request_forced].nil?) 
    "application" 
  elsif (params[:login_request_forced].present? and (params[:login_request_forced] == "" or params[:login_request_forced] == true))     
    "forced_login" 
  end 
end