diff --git a/dnet-pace-core/src/main/java/eu/dnetlib/pace/util/BlockProcessor.java b/dnet-pace-core/src/main/java/eu/dnetlib/pace/util/BlockProcessor.java
index b73b28f196..f1eefc3ead 100644
--- a/dnet-pace-core/src/main/java/eu/dnetlib/pace/util/BlockProcessor.java
+++ b/dnet-pace-core/src/main/java/eu/dnetlib/pace/util/BlockProcessor.java
@@ -131,7 +131,7 @@ public class BlockProcessor {
 
             WfConfig wf = dedupConf.getWf();
             final Field fieldsPivot = pivot.values(wf.getOrderField());
-            final String fieldPivot = (fieldsPivot == null) || fieldsPivot.isEmpty() ? null : fieldsPivot.stringValue();
+            final String fieldPivot = (fieldsPivot == null) || fieldsPivot.isEmpty() ? "" : fieldsPivot.stringValue();
 
             if (fieldPivot != null) {
                 int i = 0;