Instantiation error on the settings form

Occasionally when you go to the setting page you get this error:

HTTP Status 500 - Could not instantiate bean class [java.util.List]: Specified class is an interface.

SettingsController.getSettingsForm(...) has an argument of type List<String>, it needs to be set to a concrete class like ArrayList<String> or Vector<String>, spring attempts to create an instance of the specified argument type before passing it to the controller hence the exception