EntityReference_SelectionHandler_Views::getInstance() doesn't match signature in superclass

I'm getting

Fatal error: Declaration of EntityReference_SelectionHandler_Views::getInstance() must be compatible with that of EntityReference_SelectionHandler::getInstance() 

I'm not sure whether this might be related to PHP 5.3 or something else in our configuration but when i update the method signature from

public static function getInstance($field, $instance)

to

public static function getInstance($field, $instance = NULL, $entity_type = NULL, $entity = NULL)

The error goes away. I don't know how bad an idea it is to make the $instance optional, so please advise. Patch follows.