From c5079685bf1a99d582ceee022d6c787754b08596 Mon Sep 17 00:00:00 2001
From: Daniel Diaz <39510674+IslandRhythms@users.noreply.github.com>
Date: Tue, 18 Jul 2023 11:48:08 -0400
Subject: [PATCH 1/3] allow null values for enum

---
 lib/schema/string.js           |  2 +-
 test/schema.validation.test.js | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/lib/schema/string.js b/lib/schema/string.js
index bf1b6d85749..cb8b866c115 100644
--- a/lib/schema/string.js
+++ b/lib/schema/string.js
@@ -242,7 +242,7 @@ SchemaString.prototype.enum = function() {
 
   const vals = this.enumValues;
   this.enumValidator = function(v) {
-    return undefined === v || ~vals.indexOf(v);
+    return null == v || ~vals.indexOf(v);
   };
   this.validators.push({
     validator: this.enumValidator,
diff --git a/test/schema.validation.test.js b/test/schema.validation.test.js
index 22fab457bd1..24f7d8d9125 100644
--- a/test/schema.validation.test.js
+++ b/test/schema.validation.test.js
@@ -827,6 +827,19 @@ describe('schema', function() {
       }
     });
 
+    it('should allow null values for enum gh-3044', async function() {
+      const testSchema = new Schema({
+        name: {
+          type: String,
+          enum: ['test', null]
+        }
+      });
+      const Test = mongoose.model('allow-null' + random(), testSchema);
+      const a = new Test({ name: null });
+      const err = await a.validate().then(() => null, err => err);
+      assert.equal(err, null)
+    });
+
     it('should allow an array of subdocuments with enums (gh-3521)', async function() {
       const coolSchema = new Schema({
         votes: [{

From 886c941047e413b50def247377fbaaf77e65b0a0 Mon Sep 17 00:00:00 2001
From: Daniel Diaz <39510674+IslandRhythms@users.noreply.github.com>
Date: Tue, 18 Jul 2023 11:49:14 -0400
Subject: [PATCH 2/3] fix:lint

---
 test/schema.validation.test.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/schema.validation.test.js b/test/schema.validation.test.js
index 24f7d8d9125..73412694e2b 100644
--- a/test/schema.validation.test.js
+++ b/test/schema.validation.test.js
@@ -837,7 +837,7 @@ describe('schema', function() {
       const Test = mongoose.model('allow-null' + random(), testSchema);
       const a = new Test({ name: null });
       const err = await a.validate().then(() => null, err => err);
-      assert.equal(err, null)
+      assert.equal(err, null);
     });
 
     it('should allow an array of subdocuments with enums (gh-3521)', async function() {

From 760c18724b654b184946e540fc8f7cbf0e6024f7 Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Tue, 18 Jul 2023 16:39:31 -0400
Subject: [PATCH 3/3] Update schema.validation.test.js

---
 test/schema.validation.test.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/schema.validation.test.js b/test/schema.validation.test.js
index 73412694e2b..e467f6ea088 100644
--- a/test/schema.validation.test.js
+++ b/test/schema.validation.test.js
@@ -831,7 +831,7 @@ describe('schema', function() {
       const testSchema = new Schema({
         name: {
           type: String,
-          enum: ['test', null]
+          enum: ['test']
         }
       });
       const Test = mongoose.model('allow-null' + random(), testSchema);