It uses do/end but parts of it are white space from what I can tell.

    loop do
        case message = gets
    when Nil
        break
    when ""
        puts "Please enter a message"
    else
        puts message.upcase
    end
  end

It is not whitespace sensitive afaik. This same version works as well

    loop do
            case message = gets
                            when Nil
            break
        when ""
    puts "Please enter a message"
        else
            puts message.upcase
        end
      end

(Scrambled on purpose).