[refactor]: improve code about strategy cache

README.md

@@ -1218,11 +1218,13 @@ 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:
-        user = db.query("SELECT * FROM users WHERE user_id = {0}", user_id)
-        if user is not None:
-            key = "user.{0}".format(user_id)
-            cache.set(key, json.dumps(user))
+    if user: 
+      return user
+    
+    user = db.query("SELECT * FROM users WHERE user_id = {0}", user_id)
+    if user:
+        key = "user.{0}".format(user_id)
+        cache.set(key, json.dumps(user))
     return user
 ```