method MultiSetNonEmpty.prototype.addimport { MultiSetNonEmpty } from "https://deno.land/x/rimbu@1.0.4/multiset/custom/index.ts"; add(elem: T, amount?): WithElem<Tp, T>["nonEmpty"]Parameterselem: Toptionalamount = [UNSUPPORTED]ReturnsWithElem<Tp, T>["nonEmpty"]