Undeclared class variable

The Canto plugin uses an undeclared class variable on line 219 of includes/class-canto.php. This causes the warning:

Deprecated: Creation of dynamic property Canto::$admin is deprecated in /var/www/html/wp-content/mu-plugins/canto/includes/class-canto.php on line 219

I believe this warning can be removed with the inclusion of this code on at the top of the class file (near where the other class variables are declared):

public $admin = null;