give emptyOrSingleton() a narrower return type
give emptyOrSingleton() a narrower return type
jvasileff/ceylon.language,unratito/ceylon.language,ceylon/ceylon.language,lucaswerkmeister/ceylon.language,jvasileff/ceylon.language,ceylon/ceylon.language,unratito/ceylon.language,lucaswerkmeister/ceylon.language