Document the requirement for non-emptiness.
Document the requirement for non-emptiness.

tinkerstudent/playn,playn/playn,ruslansennov/playn2,longtaoge/playn,rachelharvey/playn,playn/playn,ruslansennov/playn2,playn/playn,tinkerstudent/playn,rachelharvey/playn,thecocce/playn-1,longtaoge/playn,thecocce/playn-1