diff --git a/dnet-pace-core/src/main/java/eu/dnetlib/pace/util/MapDocumentUtil.java b/dnet-pace-core/src/main/java/eu/dnetlib/pace/util/MapDocumentUtil.java
index 2f04767..2683c7b 100644
--- a/dnet-pace-core/src/main/java/eu/dnetlib/pace/util/MapDocumentUtil.java
+++ b/dnet-pace-core/src/main/java/eu/dnetlib/pace/util/MapDocumentUtil.java
@@ -105,6 +105,8 @@ public class MapDocumentUtil {
 
 
     public static String truncateValue(String value, int length) {
+        if (value == null)
+            return "";
 
         if (length == -1 || length > value.length())
             return value;