Bump to v4.0.0.

isNull.js

@@ -0,0 +1,24 @@
+define([], function() {
+
+  /**
+   * Checks if `value` is `null`.
+   *
+   * @static
+   * @memberOf _
+   * @category Lang
+   * @param {*} value The value to check.
+   * @returns {boolean} Returns `true` if `value` is `null`, else `false`.
+   * @example
+   *
+   * _.isNull(null);
+   * // => true
+   *
+   * _.isNull(void 0);
+   * // => false
+   */
+  function isNull(value) {
+    return value === null;
+  }
+
+  return isNull;
+});