title: Why does this Ruby method return a "void value expression" error?
body: <p>I have this simple method </p>
  
  <pre><code>def is_palindrome?(sentence)
    raise ArgumentError.new('expected string') unless sentence.is_a?(String)
    safe_sentence = sentence.gsub(/\W+/, '').downcase
    return safe_sentence == safe_sentence.reverse
  end
  
  is_palindrome?"rails"
  </code></pre>
  
  <p>When I run it I get the error <code>void value expression</code> in line 4 which is the return statement </p>
  
  <p>What's wrong here? </p>