class method self.from_session_value

# File actionpack/lib/action_dispatch/middleware/flash.rb, line 79
      def self.from_session_value(value)
        flash = case value
                when FlashHash # Rails 3.1, 3.2
                  new(value.instance_variable_get(:@flashes), value.instance_variable_get(:@used))
                when Hash # Rails 4.0
                  new(value['flashes'], value['discard'])
                else
                  new
                end

        flash.tap(&:sweep)
      end