title: Kotlin Returning Null cannot be a value of a non-null type
body: <p>I am trying to return a null value for a Kotlin function. It gives me the error <code>Null cannot be a value of a non-null type</code>.  But I want to be able to return null.  Although it looks the function can be void, it is an interface override and in this case there is no return value.</p>
  
  <pre><code>override fun call(jso: JSONObject): JSONObject {
      ...
      ...
      return null
  }
  </code></pre>
  
  <p>I guess I can mark a variable nullable using <code>?</code>. But where can I put the <code>?</code> in this case?</p>