test(populate): repro #11538

test/model.populate.test.js

@@ -10583,6 +10583,37 @@ describe('model: populate:', function() {
     assert.equal(fromDb.author.name, 'John Smithe');
   });
 
+  it('no-op when populating a single nested subdoc underneath a doc array with no ref (gh-11538) (gh-10856)', async function() {
+    const userSchema = Schema({ _id: Number, name: String, email: String, friends: [{ type: Number, ref: 'User' }] });
+    const blogPostSchema = Schema({
+      title: String,
+      people: [{
+        author: {
+          type: new Schema({ _id: Number, name: String, friends: [{ type: Number, ref: 'User' }] })
+          // ref: 'User'
+        }
+      }]
+    });
+
+    const User = db.model('User', userSchema);
+    const BlogPost = db.model('BlogPost', blogPostSchema);
+
+    await User.create({ _id: 2, name: 'Test', email: 'test@gmail.com' });
+    await User.create({ _id: 1, name: 'John Smith', email: 'test@gmail.com', friends: [2] });
+    await BlogPost.create({
+      title: 'Introduction to Mongoose',
+      people: [{
+        author: { _id: 1, name: 'John Smith', friends: [2] }
+      }]
+    });
+
+    const doc = await BlogPost.findOne().populate({
+      path: 'people',
+      populate: [{ path: 'author', populate: 'friends' }]
+    });
+    assert.strictEqual(doc.people[0].author.email, undefined);
+  });
+
   it('supports ref on array containing subdocuments (gh-10856)', async function() {
     const userSchema = Schema({ _id: Number, name: String, email: String });
     const blogPostSchema = Schema({