Create a null-prototype object for the mapping instead

index.js

@@ -1,7 +1,7 @@
 "use strict";
 
 module.exports = function splitFilter(array, ensureCategories, predicate) {
-	let results = {};
+	let results = Object.create(null);
 
 	if (ensureCategories != null) {
 		for (let category of ensureCategories) {