So siehts ganz gut aus !

node_modules/es6-set/valid-set.js

@@ -0,0 +1,8 @@
+'use strict';
+
+var isSet = require('./is-set');
+
+module.exports = function (x) {
+	if (!isSet(x)) throw new TypeError(x + " is not a Set");
+	return x;
+};