Object of class <Controller> could not be converted to string

When trying to return Response Object.
Then controller raises:

  Object of class WelcomeHomeController could not be converted to string

In Controller.class.php file, error exists at line 197

  $response->data['controller'] = $this;

I did a quick fix by

    if(is_string($response->data)) $response->data = "";

$response-&gt;data['controller'] = $this;</code>

Any idea why? and how to do better fix?