diff --git a/codes/cpp/chapter_hashing/array_hash_map.cpp b/codes/cpp/chapter_hashing/array_hash_map.cpp
index 30489b67d..6f339d6f1 100644
--- a/codes/cpp/chapter_hashing/array_hash_map.cpp
+++ b/codes/cpp/chapter_hashing/array_hash_map.cpp
@@ -47,7 +47,7 @@ class ArrayHashMap {
         int index = hashFunc(key);
         Pair *pair = buckets[index];
         if (pair == nullptr)
-            return nullptr;
+            return "";
         return pair->val;
     }
 
diff --git a/codes/cpp/chapter_hashing/hash_map_chaining.cpp b/codes/cpp/chapter_hashing/hash_map_chaining.cpp
index 2302f0c0d..1079be379 100644
--- a/codes/cpp/chapter_hashing/hash_map_chaining.cpp
+++ b/codes/cpp/chapter_hashing/hash_map_chaining.cpp
@@ -50,8 +50,8 @@ class HashMapChaining {
                 return pair->val;
             }
         }
-        // 若未找到 key 则返回 nullptr
-        return nullptr;
+        // 若未找到 key 则返回空字符串
+        return "";
     }
 
     /* 添加操作 */
diff --git a/codes/csharp/chapter_hashing/hash_map_chaining.cs b/codes/csharp/chapter_hashing/hash_map_chaining.cs
index 39270333a..fec863653 100644
--- a/codes/csharp/chapter_hashing/hash_map_chaining.cs
+++ b/codes/csharp/chapter_hashing/hash_map_chaining.cs
@@ -37,7 +37,7 @@ class HashMapChaining {
     }
 
     /* 查询操作 */
-    public string get(int key) {
+    public string? get(int key) {
         int index = hashFunc(key);
         // 遍历桶，若找到 key 则返回对应 val
         foreach (Pair pair in buckets[index]) {
diff --git a/codes/csharp/chapter_hashing/hash_map_open_addressing.cs b/codes/csharp/chapter_hashing/hash_map_open_addressing.cs
index b41a2621d..1e9df4a38 100644
--- a/codes/csharp/chapter_hashing/hash_map_open_addressing.cs
+++ b/codes/csharp/chapter_hashing/hash_map_open_addressing.cs
@@ -59,7 +59,7 @@ class HashMapOpenAddressing {
     }
 
     /* 查询操作 */
-    public string get(int key) {
+    public string? get(int key) {
         // 搜索 key 对应的桶索引
         int index = findBucket(key);
         // 若找到键值对，则返回对应 val
diff --git a/codes/python/chapter_hashing/hash_map_chaining.py b/codes/python/chapter_hashing/hash_map_chaining.py
index 069d43a53..1358650bb 100644
--- a/codes/python/chapter_hashing/hash_map_chaining.py
+++ b/codes/python/chapter_hashing/hash_map_chaining.py
@@ -29,7 +29,7 @@ class HashMapChaining:
         """负载因子"""
         return self.size / self.capacity
 
-    def get(self, key: int) -> str:
+    def get(self, key: int) -> str | None:
         """查询操作"""
         index = self.hash_func(key)
         bucket = self.buckets[index]
diff --git a/docs/chapter_hashing/hash_algorithm.md b/docs/chapter_hashing/hash_algorithm.md
index e9f8bb2b8..4aac985bf 100644
--- a/docs/chapter_hashing/hash_algorithm.md
+++ b/docs/chapter_hashing/hash_algorithm.md
@@ -475,7 +475,6 @@ $$
     node.borrow().val.hash(&mut hasher);
     let hash = hasher.finish();
     // 节点对象 RefCell { value: ListNode { val: 42, next: None } } 的哈希值为15387811073369036852
-
     ```
 
 === "C"
diff --git a/docs/chapter_tree/avl_tree.md b/docs/chapter_tree/avl_tree.md
index 89472f22c..8628267ac 100644
--- a/docs/chapter_tree/avl_tree.md
+++ b/docs/chapter_tree/avl_tree.md
@@ -156,7 +156,7 @@ AVL 树既是二叉搜索树也是平衡二叉树，同时满足这两类二叉
     use std::rc::Rc;
     use std::cell::RefCell;
 
-    /* AVL 树节点类型 */
+    /* AVL 树节点结构体 */
     struct TreeNode {
         val: i32,                               // 节点值
         height: i32,                            // 节点高度
@@ -165,7 +165,7 @@ AVL 树既是二叉搜索树也是平衡二叉树，同时满足这两类二叉
     }
 
     impl TreeNode {
-        /* AVL 树节点构造方法 */
+        /* 构造方法 */
         fn new(val: i32) -> Rc<RefCell<Self>> {
             Rc::new(RefCell::new(Self {
                 val,