diff --git a/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/sx/graph/SparkResolveRelation.scala b/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/sx/graph/SparkResolveRelation.scala
index 11d026f02..9e7963b2a 100644
--- a/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/sx/graph/SparkResolveRelation.scala
+++ b/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/sx/graph/SparkResolveRelation.scala
@@ -48,7 +48,7 @@ object SparkResolveRelation {
       m =>
         val sourceResolved = m._2
         val currentRelation = m._1._2
-        if (sourceResolved!=null && sourceResolved._2.nonEmpty)
+        if (sourceResolved!=null && sourceResolved._2!=null && sourceResolved._2.nonEmpty)
           currentRelation.setSource(sourceResolved._2)
         currentRelation
     }.write