diff --git a/src/api/endpoints/drive/folders/update.ts b/src/api/endpoints/drive/folders/update.ts
index eec2757878..4f2e3d2a7a 100644
--- a/src/api/endpoints/drive/folders/update.ts
+++ b/src/api/endpoints/drive/folders/update.ts
@@ -4,7 +4,7 @@
 import $ from 'cafy';
 import DriveFolder from '../../../models/drive-folder';
 import { isValidFolderName } from '../../../models/drive-folder';
-import serialize from '../../../serializers/drive-file';
+import serialize from '../../../serializers/drive-folder';
 import event from '../../../event';
 
 /**
diff --git a/src/api/serializers/post.ts b/src/api/serializers/post.ts
index 5788b226f4..5a63384f0e 100644
--- a/src/api/serializers/post.ts
+++ b/src/api/serializers/post.ts
@@ -57,6 +57,8 @@ const self = async (
 		_post = deepcopy(post);
 	}
 
+	if (!_post) throw 'invalid post arg.';	
+
 	const id = _post._id;
 
 	// Rename _id to id
diff --git a/src/api/serializers/user.ts b/src/api/serializers/user.ts
index d00f073897..0d24d6cc04 100644
--- a/src/api/serializers/user.ts
+++ b/src/api/serializers/user.ts
@@ -56,6 +56,8 @@ export default (
 		_user = deepcopy(user);
 	}
 
+	if (!_user) return reject('invalid user arg.');
+
 	// Me
 	const meId: mongo.ObjectID = me
 		? mongo.ObjectID.prototype.isPrototypeOf(me)