+ throw new MysteryBoxError('Invalid default flag value');
+ }
+ }
+
+
+ /**
+ * Return an array containing x if x is something and not an array
+ * @param {*} x
+ */
+ static _ensureArray(x) {
+ if (x === undefined) {
+ return [];
+ }
+ if (!Array.isArray(x)) {
+ return Array(x);