From 02afe2ba7937cfb11745758cf04a582c8dd41332 Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Tue, 2 Jul 2024 09:49:55 -0400
Subject: [PATCH 1/2] feat: allow setting array default value to `null`

Fix #6691
---
 docs/faq.md         | 6 +++---
 lib/schema/array.js | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/docs/faq.md b/docs/faq.md
index 8ae6a441b35..a0d493bc879 100644
--- a/docs/faq.md
+++ b/docs/faq.md
@@ -314,7 +314,7 @@ const Kitten = connection.model('Kitten', kittySchema);
 
 <a class="anchor" href="#array-defaults">**Q**</a>. How can I change mongoose's default behavior of initializing an array path to an empty array so that I can require real data on document creation?
 
-**A**. You can set the default of the array to a function that returns `undefined`.
+**A**. You can set the default of the array to `undefined`.
 
 ```javascript
 const CollectionSchema = new Schema({
@@ -329,13 +329,13 @@ const CollectionSchema = new Schema({
 
 <a class="anchor" href="#initialize-array-path-null">**Q**</a>. How can I initialize an array path to `null`?
 
-**A**. You can set the default of the array to a function that returns `null`.
+**A**. You can set the default of the array to [`null`](https://masteringjs.io/tutorials/fundamentals/null).
 
 ```javascript
 const CollectionSchema = new Schema({
   field1: {
     type: [String],
-    default: () => { return null; }
+    default: null
   }
 });
 ```
diff --git a/lib/schema/array.js b/lib/schema/array.js
index 67fe713a99b..00774ee3147 100644
--- a/lib/schema/array.js
+++ b/lib/schema/array.js
@@ -111,7 +111,7 @@ function SchemaArray(key, cast, options, schemaOptions) {
     fn = typeof defaultArr === 'function';
   }
 
-  if (!('defaultValue' in this) || this.defaultValue !== void 0) {
+  if (!('defaultValue' in this) || this.defaultValue != null) {
     const defaultFn = function() {
       // Leave it up to `cast()` to convert the array
       return fn

From b2f7ee4e02ba541129f08ee12a8ad1e965a7c0dc Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Thu, 4 Jul 2024 09:30:26 -0400
Subject: [PATCH 2/2] test: add test for setting array default value to null
 re: #6691

---
 test/document.test.js | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/test/document.test.js b/test/document.test.js
index f633a2ca75e..344ae9e5a7f 100644
--- a/test/document.test.js
+++ b/test/document.test.js
@@ -3198,6 +3198,23 @@ describe('document', function() {
       assert.ok(!('names' in doc));
     });
 
+    it('can set array default to null (gh-14717)', async function() {
+      const schema = new Schema({
+        names: {
+          type: [String],
+          default: null
+        }
+      });
+
+      const Model = db.model('Test', schema);
+      const m = new Model();
+      assert.strictEqual(m.names, null);
+      await m.save();
+
+      const doc = await Model.collection.findOne({ _id: m._id });
+      assert.strictEqual(doc.names, null);
+    });
+
     it('validation works when setting array index (gh-3816)', async function() {
       const mySchema = new mongoose.Schema({
         items: [