commit_flash

# File actionpack/lib/action_dispatch/middleware/flash.rb, line 59
      def commit_flash # :nodoc:
        session    = self.session || {}
        flash_hash = self.flash_hash

        if flash_hash && (flash_hash.present? || session.key?('flash'))
          session["flash"] = flash_hash.to_session_value
          self.flash = flash_hash.dup
        end

        if (!session.respond_to?(:loaded?) || session.loaded?) && # (reset_session uses {}, which doesn't implement #loaded?)
            session.key?('flash') && session['flash'].nil?
          session.delete('flash')
        end
      end