Add _.isNil function.

lodash.js

@@ -854,7 +854,7 @@
      * `has`, `identity`, `includes`, `indexOf`, `inRange`, `isArguments`,
      * `isArray`, `isBoolean`, `isDate`, `isElement`, `isEmpty`, `isEqual`,
      * `isEqualWith`, `isError`, `isFinite` `isFunction`, `isMatch`, `isMatchWith`,
-     * `isNative`, `isNaN`, `isNull`, `isNumber`, `isObject`, `isPlainObject`,
+     * `isNative`, `isNaN`, `isNil`, `isNull`, `isNumber`, `isObject`, `isPlainObject`,
      * `isRegExp`, `isString`, `isUndefined`, `isTypedArray`, `join`, `kebabCase`,
      * `last`, `lastIndexOf`, `lt`, `lte`, `max`, `min`, `noConflict`, `noop`,
      * `now`, `pad`, `padLeft`, `padRight`, `parseInt`, `pop`, `random`, `reduce`,
@@ -8273,6 +8273,35 @@
       return value === null;
     }
 
+    /**
+     * Checks if `value` is `null` or `undefined`.
+     *
+     * @static
+     * @memberOf _
+     * @category Lang
+     * @param {*} value The value to check.
+     * @returns {boolean} Returns `true` if `value` is `null` or `undefined`, else `false`.
+     * @example
+     *
+     * _.isNil(null);
+     * // => true
+     *
+     * _.isNil();
+     * // => true
+     *
+     * _.isNil(undefined);
+     * // => true
+     *
+     * _.isNil(NaN);
+     * // => false
+     *
+     * _.isNil(void 0);
+     * // => false
+     */
+    function isNil(value) {
+      return value == null;
+    }
+
     /**
      * Checks if `value` is classified as a `Number` primitive or object.
      *
@@ -11515,6 +11544,7 @@
     lodash.isMatchWith = isMatchWith;
     lodash.isNaN = isNaN;
     lodash.isNative = isNative;
+    lodash.isNil = isNil;
     lodash.isNull = isNull;
     lodash.isNumber = isNumber;
     lodash.isObject = isObject;

test/test.js

@@ -7723,6 +7723,58 @@
 
   /*--------------------------------------------------------------------------*/
 
+  QUnit.module('lodash.isNil');
+
+  (function() {
+    var args = arguments;
+
+    test('should return `true` for nulls', 1, function() {
+      strictEqual(_.isNil(null), true);
+    });
+
+    test('should return `true` for undefinitions', 2, function() {
+      strictEqual(_.isNil(), true);
+      strictEqual(_.isNil(undefined), true);
+    });
+
+    test('should return `false` for non-nils', 13, function() {
+      var expected = _.map(falsey, function(value) {
+        return undefined === value || null === value;
+      });
+
+      var actual = _.map(falsey, function(value) {
+        return _.isNil(value);
+      });
+
+      deepEqual(actual, expected);
+
+      strictEqual(_.isNull(args), false);
+      strictEqual(_.isNull([1, 2, 3]), false);
+      strictEqual(_.isNull(true), false);
+      strictEqual(_.isNull(new Date), false);
+      strictEqual(_.isNull(new Error), false);
+      strictEqual(_.isNull(_), false);
+      strictEqual(_.isNull(slice), false);
+      strictEqual(_.isNull({ 'a': 1 }), false);
+      strictEqual(_.isNull(1), false);
+      strictEqual(_.isNull(NaN), false);
+      strictEqual(_.isNull(/x/), false);
+      strictEqual(_.isNull('a'), false);
+    });
+
+    test('should work with nulls from another realm', 2, function() {
+      if (_._object) {
+        strictEqual(_.isNil(_._null), true);
+        strictEqual(_.isNil(_._undefined), true);
+      }
+      else {
+        skipTest();
+      }
+    });
+  }(1, 2, 3));
+
+  /*--------------------------------------------------------------------------*/
+
   QUnit.module('lodash.isNumber');
 
   (function() {
@@ -17043,6 +17095,7 @@
       'isFinite',
       'isFunction',
       'isNaN',
+      'isNil',
       'isNull',
       'isNumber',
       'isObject',
@@ -17269,7 +17322,7 @@
 
     var acceptFalsey = _.difference(allMethods, rejectFalsey);
 
-    test('should accept falsey arguments', 223, function() {
+    test('should accept falsey arguments', 224, function() {
       var emptyArrays = _.map(falsey, _.constant([]));
 
       _.each(acceptFalsey, function(methodName) {