From 50386359d8439e46561265f9639e901d3acb285e Mon Sep 17 00:00:00 2001
From: Valeri Karpov <valkar207@gmail.com>
Date: Sat, 20 May 2017 10:40:58 -0600
Subject: [PATCH] fix(schema): enforce that _id is never null

Re: #5236 mongodb/node-mongodb-native#517
---
 lib/model.js           |  2 +-
 lib/schema/objectid.js |  3 +++
 test/document.test.js  | 10 ++++++++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/lib/model.js b/lib/model.js
index 27caf0f4dc0..05a068bad8e 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -126,7 +126,7 @@ Model.prototype.$__handleSave = function(options, callback) {
 
     var obj = this.toObject(toObjectOptions);
 
-    if (!utils.object.hasOwnProperty(obj || {}, '_id')) {
+    if ((obj || {})._id == null) {
       // documents must have an _id else mongoose won't know
       // what to update later if more changes are made. the user
       // wouldn't know what _id was generated by mongodb either
diff --git a/lib/schema/objectid.js b/lib/schema/objectid.js
index 6f684191c90..f0dd9fdc42a 100644
--- a/lib/schema/objectid.js
+++ b/lib/schema/objectid.js
@@ -196,6 +196,9 @@ function defaultId() {
 }
 
 function resetId(v) {
+  if (v == null) {
+    return new oid();
+  }
   this.$__._id = null;
   return v;
 }
diff --git a/test/document.test.js b/test/document.test.js
index c8be117e84b..37af387e0fa 100644
--- a/test/document.test.js
+++ b/test/document.test.js
@@ -4162,6 +4162,16 @@ describe('document', function() {
       });
     });
 
+    it('null _id (gh-5236)', function(done) {
+      var childSchema = new mongoose.Schema({});
+
+      var M = db.model('gh5236', childSchema);
+
+      var m = new M({ _id: null });
+      assert.ok(m._id);
+      done();
+    });
+
     it('modify multiple subdoc paths (gh-4405)', function(done) {
       var ChildObjectSchema = new Schema({
         childProperty1: String,