title: How to declare a nullable function Parameter in kotlin
body: <p>For example:</p>
  
  <pre><code>fun f(func: () -&gt; Any?)
  </code></pre>
  
  <p>Parameter func means a function which returns Any? type. But how to make func nullable like:</p>
  
  <pre><code>fun f( (func: () -&gt; Any?)? )
  </code></pre>