return null to abort builtin
return null to abort builtin

kkkyyy03/scssphp,webdevid/scssphp,g105b/scssphp,webdevid/scssphp,dleffler/scssphp,dleffler/scssphp,leafo/scssphp,leafo/scssphp,webdevid/scssphp,g105b/scssphp,dleffler/scssphp,g105b/scssphp,leafo/scssphp