Fix IDE warnings (#12085)

### What problem does this PR solve?

As title

### Type of change

- [x] Refactoring

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

api/apps/__init__.py

@@ -108,7 +108,7 @@ def _load_user():
     authorization = request.headers.get("Authorization")
     g.user = None
     if not authorization:
-        return
+        return None
 
     try:
         access_token = str(jwt.loads(authorization))