diff --git a/java/Chapter 1/Question1_1/Question.java b/java/Chapter 1/Question1_1/Question.java
index 5c5b38e8..9590ec28 100644
--- a/java/Chapter 1/Question1_1/Question.java	
+++ b/java/Chapter 1/Question1_1/Question.java	
@@ -3,6 +3,9 @@
 public class Question {
 
 	public static boolean isUniqueChars(String str) {
+        if (null==str) {
+            return false;
+        }
 		if (str.length() > 128) {
 			return false;
 		}
@@ -16,6 +19,9 @@ public static boolean isUniqueChars(String str) {
 	}
 	
 	public static boolean isUniqueChars2(String str) {
+        if (null==str) {
+            return false;
+        }
 		if (str.length() > 128) {
 			return false;
 		}