CI3 and Flexi Auth __get() error

Hi,
I'm upgrading to CI 3 and I'm using Flexi Auth library.

I get the error:

Message: Declaration of Flexi_auth_lite_model::__get() should be compatible with that of CI_Model::__get()

and the code in Filename: models/Flexi_auth_lite_model.php is:

PHP Code:

public function & __get($key)
 {
 $CI =& get_instance();
 return $CI->$key;
 
 } 


any suggestion?

Thanks