Rails - Custom 404 and 500 pages and the exception_notification gem

application_controller.rb

class ApplicationController < ActionController::Base
  # ...

  private

  # ...

  def notify(exception)
    ExceptionNotifier::Notifier.exception_notification(request.env, exception,
      data: {message: 'an error happened'}).deliver
  end

  # ...
end

application_controller_other.rb

class ApplicationController < ActionController::Base
  # ...

  private

  def render_404(exception)
    notify exception
    # ...
  end

  def render_500(exception)
    notify exception
    # ...
  end
  # ...
end