diff --git a/notes/剑指 offer 题解.md b/notes/剑指 offer 题解.md
index 5e2b2553..b785b54d 100644
--- a/notes/剑指 offer 题解.md	
+++ b/notes/剑指 offer 题解.md	
@@ -1017,6 +1017,8 @@ public boolean match(char[] str, char[] pattern) {
 
 ```java
 public boolean isNumeric(char[] str) {
+    if (str == null)
+        return false;
     return new String(str).matches("[+-]?\\d*(\\.\\d+)?([eE][+-]?\\d+)?");
 }
 ```