Ensure _.omit doesn’t mutate object with deep paths. [closes #2912]

lodash.js

@@ -5632,8 +5632,8 @@
      * @param {string} key The key of the property to inspect.
      * @returns {*} Returns the uncloned value or `undefined` to defer cloning to `_.cloneDeep`.
      */
-    function customOmitClone(value, key) {
-      return (key !== undefined && isPlainObject(value)) ? undefined : value;
+    function customOmitClone(value) {
+      return isPlainObject(value) ? undefined : value;
     }
 
     /**

test/test.js

@@ -16450,6 +16450,16 @@
 
       assert.deepEqual(_.omit(object, args), { 'b': 2, 'd': 4 });
     });
+
+    QUnit.test('should not mutate `object`', function(assert) {
+      assert.expect(4);
+
+      lodashStable.each(['a', ['a'], 'a.b', ['a.b']], function(path) {
+        var object = { 'a': { 'b': 2 } };
+        _.omit(object, path);
+        assert.deepEqual(object, { 'a': { 'b': 2 } });
+      });
+    });
   }());
 
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