diff --git a/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/base/AMutableString.java b/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/base/AMutableString.java
index 33217cd..b2a4a5e 100644
--- a/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/base/AMutableString.java
+++ b/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/base/AMutableString.java
@@ -20,11 +20,16 @@
 
 public class AMutableString extends AString {
 
+    private static final long serialVersionUID = 1L;
+
     public AMutableString(String value) {
         super(value);
     }
 
     public void setValue(String value) {
+        if (value == null) {
+            throw new NullPointerException();
+        }
         this.value = value;
     }
 }