diff --git a/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/oa/graph/clean/cfhb/CleanCfHbSparkJob.java b/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/oa/graph/clean/cfhb/CleanCfHbSparkJob.java
index eb7325af5..f48226d71 100644
--- a/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/oa/graph/clean/cfhb/CleanCfHbSparkJob.java
+++ b/dhp-workflows/dhp-graph-mapper/src/main/java/eu/dnetlib/dhp/oa/graph/clean/cfhb/CleanCfHbSparkJob.java
@@ -13,6 +13,7 @@ import java.util.stream.Stream;
 import org.apache.commons.io.IOUtils;
 import org.apache.commons.lang3.StringUtils;
 import org.apache.spark.SparkConf;
+import org.apache.spark.api.java.function.FilterFunction;
 import org.apache.spark.api.java.function.FlatMapFunction;
 import org.apache.spark.api.java.function.MapFunction;
 import org.apache.spark.api.java.function.MapGroupsFunction;
@@ -105,6 +106,7 @@ public class CleanCfHbSparkJob {
 		resolved
 			.joinWith(md, resolved.col("cfhb").equalTo(md.col("duplicateId")))
 			.map(asIdCfHbMapping(), Encoders.bean(IdCfHbMapping.class))
+			.filter((FilterFunction<IdCfHbMapping>) m -> Objects.nonNull(m.getMasterId()))
 			.write()
 			.mode(SaveMode.Overwrite)
 			.json(resolvedPath);
@@ -134,9 +136,15 @@ public class CleanCfHbSparkJob {
 
 	private static MapFunction<Tuple2<IdCfHbMapping, MasterDuplicate>, IdCfHbMapping> asIdCfHbMapping() {
 		return t -> {
-			t._1().setMasterId(t._2().getMasterId());
-			t._1().setMasterName(t._2().getMasterName());
-			return t._1();
+			final IdCfHbMapping mapping = t._1();
+			Optional
+				.ofNullable(t._2())
+				.ifPresent(t2 -> {
+					mapping.setMasterId(t2.getMasterId());
+					mapping.setMasterName(t2.getMasterName());
+
+				});
+			return mapping;
 		};
 	}