def set_message_for(exception, env)
      session = env[ActionDispatch::Request::Session::ENV_SESSION_KEY] || {}
      env[ActionDispatch::Flash::KEY] ||= ActionDispatch::Flash::FlashHash.from_session_value session['flash']
      flash = env[ActionDispatch::Flash::KEY]
      flash[:alert] = exception.message
    end
def set_message_for(exception, env)
      session = env[ActionDispatch::Request::Session::ENV_SESSION_KEY] || {}
      env[ActionDispatch::Flash::KEY] ||= ActionDispatch::Flash::FlashHash.from_session_value session['flash']
      flash = env[ActionDispatch::Flash::KEY]
      flash[:alert] = exception.message
    end
Set flash error message
 @param exception [Exception]
 @param env [Hash] @see http://www.rubydoc.info/github/rack/rack/master/file/SPEC