From 78982f3074cbb1c9522ac8b9e3ebec269f94018c Mon Sep 17 00:00:00 2001
From: John-David Dalton <john.david.dalton@gmail.com>
Date: Thu, 21 Jan 2016 01:13:21 -0600
Subject: [PATCH] Ensure `_.concat` returns an empty array for nullish `array`
 values. [closes #1856]

---
 lodash.js    |  3 +++
 test/test.js | 15 +++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/lodash.js b/lodash.js
index f511c67d6..abded307b 100644
--- a/lodash.js
+++ b/lodash.js
@@ -5336,6 +5336,9 @@
      * // => [1]
      */
     var concat = rest(function(array, values) {
+      if (array == null) {
+        return [];
+      }
       values = baseFlatten(values);
       return arrayConcat(isArray(array) ? array : [Object(array)], values);
     });
diff --git a/test/test.js b/test/test.js
index ff1f771f8..c3256fada 100644
--- a/test/test.js
+++ b/test/test.js
@@ -2827,6 +2827,21 @@
       assert.deepEqual(array, [1]);
     });
 
+    QUnit.test('should return an empty array when `array` is nullish', function(assert) {
+      assert.expect(1);
+
+      var values = [, null, undefined],
+          expected = lodashStable.map(values, alwaysEmptyArray);
+
+      var actual = lodashStable.map(values, function(value, index) {
+        try {
+          return index ? _.concat(value) : _.concat();
+        } catch (e) {}
+      });
+
+      assert.deepEqual(actual, expected);
+    });
+
     QUnit.test('should treat sparse arrays as dense', function(assert) {
       assert.expect(3);