title: yield(:title) in Ruby on Rails is never equal to false for some reason
body: <pre><code>#layouts/application.html.haml
      %title
       = yield(:title) || "Default page title"
       = " | DefaultSite.com"
  
  
  #application_helper.rb
   def title(page_title)
      content_for(:title) { page_title }
    end
  </code></pre>
  
  <p>Even if I don't set a <code>title</code> (helper method) for a page, <code>"Default page title"</code> never shows. Instead of it, <code>""</code> (the value of <code>yield(:title)</code>) appears for some reason.</p>
  
  <p>Why is this happening?</p>