refs #272 map-merge support for empty lists (indistinguishable from an empty map)
refs #272 map-merge support for empty lists (indistinguishable from an empty map)

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