fix(document): recursively clear modified subpaths when setting deeply nested subdoc to null

lib/helpers/document/cleanModifiedSubpaths.js

@@ -25,11 +25,21 @@ module.exports = function cleanModifiedSubpaths(doc, path, options) {
       ++deleted;
 
       if (doc.$isSubdocument) {
-        const owner = doc.ownerDocument();
-        const fullPath = doc.$__fullPath(modifiedPath);
-        owner.$__.activePaths.clearPath(fullPath);
+        cleanParent(doc, modifiedPath);
       }
     }
   }
   return deleted;
 };
+
+function cleanParent(doc, path, seen = new Set()) {
+  if (seen.has(doc)) {
+    throw new Error('Infinite subdocument loop: subdoc with _id ' + doc._id + ' is a parent of itself');
+  }
+  const parent = doc.$parent();
+  const newPath = doc.$__pathRelativeToParent(void 0, false) + '.' + path;
+  parent.$__.activePaths.clearPath(newPath);
+  if (parent.$isSubdocument) {
+    cleanParent(parent, newPath, seen);
+  }
+}

test/document.test.js

@@ -13978,6 +13978,84 @@ describe('document', function() {
     assert.ok(Buffer.isBuffer(reloaded.pdfSettings.fileContent));
     assert.strictEqual(reloaded.pdfSettings.fileContent.toString('utf8'), 'hello');
   });
+
+  it('clears modified subpaths when setting deeply nested subdoc to null (gh-14952)', async function() {
+    const currentMilestoneSchema = new Schema(
+      {
+        id: { type: String, required: true }
+      },
+      {
+        _id: false
+      }
+    );
+
+    const milestoneSchema = new Schema(
+      {
+        current: {
+          type: currentMilestoneSchema,
+          required: true
+        }
+      },
+      {
+        _id: false
+      }
+    );
+
+    const campaignSchema = new Schema(
+      {
+        milestones: {
+          type: milestoneSchema,
+          required: false
+        }
+      },
+      {
+        _id: false
+      }
+    );
+    const questSchema = new Schema(
+      {
+        campaign: { type: campaignSchema, required: false }
+      },
+      {
+        _id: false
+      }
+    );
+
+    const parentSchema = new Schema({
+      quests: [questSchema]
+    });
+
+    const ParentModel = db.model('Parent', parentSchema);
+    const doc = new ParentModel({
+      quests: [
+        {
+          campaign: {
+            milestones: {
+              current: {
+                id: 'milestone1'
+              }
+            }
+          }
+        }
+      ]
+    });
+
+    await doc.save();
+
+    // Set the nested schema to null
+    doc.quests[0].campaign.milestones.current = {
+      id: 'milestone1'
+    };
+    doc.quests[0].campaign.milestones.current = {
+      id: ''
+    };
+
+    doc.quests[0].campaign.milestones = null;
+    await doc.save();
+
+    const fromDb = await ParentModel.findById(doc._id).orFail();
+    assert.strictEqual(fromDb.quests[0].campaign.milestones, null);
+  });
 });
 
 describe('Check if instance function that is supplied in schema option is available', function() {