title: Cannot call value of non-function type
body: <p>Having issues trying to convert this to Swift 3.0.</p>
  
  <p>I have: </p>
  
  <pre><code>public typealias CustomCompletionBlock = (_ image: UIImage?, _ error: Error?) -&gt; Void
  public var completionBlock : CustomCompletionBlock!
  </code></pre>
  
  <p>Later on in my code I want to set <code>completionBlock</code> e.g.:</p>
  
  <pre><code>self.completionBlock(image: nil, error: error)
  </code></pre>
  
  <p>But I get the error <strong><em>"Cannot call value of non-function type"</em></strong>. What am I doing wrong here?</p>