Bump to v4.0.0.

isUndefined.js

@@ -0,0 +1,21 @@
+/**
+ * Checks if `value` is `undefined`.
+ *
+ * @static
+ * @memberOf _
+ * @category Lang
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is `undefined`, else `false`.
+ * @example
+ *
+ * _.isUndefined(void 0);
+ * // => true
+ *
+ * _.isUndefined(null);
+ * // => false
+ */
+function isUndefined(value) {
+  return value === undefined;
+}
+
+export default isUndefined;