Reverse world in sentence with rack and form

gistfile1.txt

# my_app_ter.ru

use Rack::MethodOverride

map '/' do
  form = <<-HERE
  <form action="/reverse_word" method="post">
  <input name="_method" type="hidden" value="put" />
  <input name="sentence" type="text" value="" />
  <input type="submit" value="Reverse the words order">
  </form>
  HERE
  run lambda {|env| [200, {"Content-Type" => "text/html"}, [form]] }
end

map '/reverse_word' do
  run lambda {|env|
    req = Rack::Request.new env
    res = Rack::Response.new

    if(req.params['sentence'].class==NilClass || req.params['sentence'].split(" ").size < 2)
        res.write("Please enter one sentence with at least two words to reverse it")
    else(req.put?)
      res.write("#{req.params['sentence'].split(' ').reverse.join(' ')}")
    end
    res.finish
  }
end

# usage: rackup my_app_ter.ru