title: Capistrano 3 alternative to exists? capistrano 2 method
body: <p>In Capistrano 2 it was pretty easy to check if variable was set with </p>
  
  <pre><code>exists?(:variable)
  </code></pre>
  
  <p>In capistrano 3 exists? method was removed as I get 'undefined method exists?' as i try to run the task.</p>
  
  <p>So what is the alternative way to check if variable was set in capistrano 3?</p>