title: Undefined method `upcase' for nil:NilClass (NoMethodError) - Ruby 1.9.3
body: <p>I'm really beginner in ruby, trying to write a simple program to detect uppercase input. I use ruby-1.9.3-p125 now. So, I'm trying to compile this:</p>
  
  <pre><code># coding: utf-8
  puts 'hello! enter something:'
  while req!=req.upcase
      req=gets.chomp
      if req == req.upcase
          puts "This is UpperCase!"
      else
          puts "Not UpperCase :( Try again!"
      end
  end
  puts "GoodBye!"
  </code></pre>
  
  <p>And I get a such error:</p>
  
  <pre><code>app1.rb:4:in `&lt;main&gt;': undefined method `upcase' for nil:NilClass (NoMethodError)
  </code></pre>
  
  <p>Maybe I should include any lib or smth like this? BTW, "UpCase".upcase` works good.</p>