title: How to check if a variable is nil
body: <p>I have a variable </p>
  
  <pre><code>var a: [AnyObject? -&gt; Void] 
  </code></pre>
  
  <p>and I am adding data in to it by append method. Now I want to check if the variable is nil or not. I tried using <code>[]</code> but not working and also tried <code>""</code>, this also not working, can anyone tell what is the meaning of this variable and how to check if it is nil. </p>