title: Ruby `downcase!` returns `nil`
body: <p>With this code:</p>
  
  <pre><code>input = gets.chomp.downcase!
  puts input
  </code></pre>
  
  <p>if there is at least one uppercase letter in the input, the input will be put on screen, freed of its uppercases. But if the input has no uppercase letter, it will put <code>nil</code>, like if nothing was written.</p>
  
  <p>I want my input to be fully downcased; if it is a string with no uppercase letter, it should return the same string.</p>
  
  <p>I thought about something like this:</p>
  
  <pre><code>input = gets.chomp
  if input.include(uppercase) then input.downcase! end
  </code></pre>
  
  <p>But this doesn't work. I hope someone has an idea on how I should do this.</p>