FIX Import Closure class for type checking, and only set sort if the sort field exists
FIX Import Closure class for type checking, and only set sort if the sort field exists

kinglozzer/silverstripe-gridfieldextensions,symbiote/silverstripe-gridfieldextensions,silverstripe-australia/silverstripe-gridfieldextensions,dhensby/silverstripe-gridfieldextensions,silverstripe-australia/silverstripe-gridfieldextensions,dhensby/silverstripe-gridfieldextensions,symbiote/silverstripe-gridfieldextensions,kinglozzer/silverstripe-gridfieldextensions