diff --git a/src/fr/inrialpes/exmo/ontowrap/Annotation.java b/src/fr/inrialpes/exmo/ontowrap/Annotation.java
index eead02c232fc7547bc036cc424947a116788208a..709423d0a8f389804cfc8d7f49406d77c3fad3f0 100644
--- a/src/fr/inrialpes/exmo/ontowrap/Annotation.java
+++ b/src/fr/inrialpes/exmo/ontowrap/Annotation.java
@@ -48,7 +48,7 @@ public class Annotation {
     }
     
     public int hashCode() {
-	return value.hashCode();
+	return value==null?0:value.hashCode();
     }
     
     public boolean equals(Object o) {