[refactor]: improve code about strategy cache

README.md

@@ -1218,9 +1218,11 @@ The application is responsible for reading and writing from storage.  The cache
 ```python
 def get_user(self, user_id):
     user = cache.get("user.{0}", user_id)
-    if user is None:
+    if user: 
+      return user
+    
     user = db.query("SELECT * FROM users WHERE user_id = {0}", user_id)
-        if user is not None:
+    if user:
         key = "user.{0}".format(user_id)
         cache.set(key, json.dumps(user))
     return user