diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Dataset.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Dataset.java
index f33b11d21..70a6d1f31 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Dataset.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Dataset.java
@@ -79,6 +79,11 @@ public class Dataset extends Result implements Serializable {
     @Override
     public void mergeFrom(OafEntity e) {
         super.mergeFrom(e);
+
+        if (!Dataset.class.isAssignableFrom(e.getClass())){
+            return;
+        }
+
         final Dataset d = (Dataset) e;
 
         storagedate = d.getStoragedate() != null && compareTrust(this, e)<0? d.getStoragedate() : storagedate;
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Datasource.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Datasource.java
index 08936cc29..c8d9736c5 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Datasource.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Datasource.java
@@ -367,6 +367,10 @@ public class Datasource extends OafEntity implements Serializable {
     public void mergeFrom(OafEntity e) {
         super.mergeFrom(e);
 
+        if (!Datasource.class.isAssignableFrom(e.getClass())){
+            return;
+        }
+
         Datasource d = (Datasource)e;
 
         datasourcetype = d.getDatasourcetype() != null && compareTrust(this, e)<0? d.getDatasourcetype() : datasourcetype;
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Organization.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Organization.java
index ab3730f52..a73a7f845 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Organization.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Organization.java
@@ -170,6 +170,11 @@ public class Organization extends OafEntity implements Serializable {
     @Override
     public void mergeFrom(OafEntity e) {
         super.mergeFrom(e);
+
+        if (!Organization.class.isAssignableFrom(e.getClass())){
+            return;
+        }
+
         final Organization o = (Organization) e;
         legalshortname = o.getLegalshortname() != null && compareTrust(this, e)<0? o.getLegalshortname() : legalshortname;
         legalname = o.getLegalname() != null && compareTrust(this, e)<0 ? o.getLegalname() : legalname;
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OtherResearchProduct.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OtherResearchProduct.java
index 9d93d73d3..cc36817bb 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OtherResearchProduct.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/OtherResearchProduct.java
@@ -40,6 +40,10 @@ public class OtherResearchProduct extends Result implements Serializable {
     public void mergeFrom(OafEntity e) {
         super.mergeFrom(e);
 
+        if (!OtherResearchProduct.class.isAssignableFrom(e.getClass())){
+            return;
+        }
+
         OtherResearchProduct o = (OtherResearchProduct)e;
 
         contactperson = mergeLists(contactperson, o.getContactperson());
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Project.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Project.java
index 8d9b8fd2d..023be8fc0 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Project.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Project.java
@@ -270,6 +270,11 @@ public class Project extends OafEntity implements Serializable {
     @Override
     public void mergeFrom(OafEntity e) {
         super.mergeFrom(e);
+
+        if (!Project.class.isAssignableFrom(e.getClass())){
+            return;
+        }
+
         Project p = (Project)e;
 
             websiteurl= p.getWebsiteurl()!= null && compareTrust(this,e)<0?p.getWebsiteurl():websiteurl;
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Publication.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Publication.java
index 0e3291e16..20a0b2121 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Publication.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Publication.java
@@ -20,6 +20,10 @@ public class Publication extends Result implements Serializable {
     public void mergeFrom(OafEntity e) {
         super.mergeFrom(e);
 
+        if (!Publication.class.isAssignableFrom(e.getClass())){
+            return;
+        }
+
         Publication p = (Publication) e;
 
         if (p.getJournal() != null && compareTrust(this, e)<0)
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java
index 6738b8693..768fea19f 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Relation.java
@@ -1,8 +1,6 @@
 package eu.dnetlib.dhp.schema.oaf;
 
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Objects;
+import java.util.*;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -78,9 +76,12 @@ public class Relation extends Oaf {
 		checkArgument(Objects.equals(getSubRelType(), r.getSubRelType()),"subRelType(s) must be equal");
 		checkArgument(Objects.equals(getRelClass(), r.getRelClass()),"relClass(es) must be equal");
 
-		setCollectedFrom(Stream.concat(getCollectedFrom().stream(), r.getCollectedFrom().stream())
-				.distinct() // relies on KeyValue.equals
-				.collect(Collectors.toList()));
+		setCollectedFrom(
+				Stream
+						.concat(Optional.ofNullable(getCollectedFrom()).map(Collection::stream).orElse(Stream.empty()),
+								Optional.ofNullable(r.getCollectedFrom()).map(Collection::stream).orElse(Stream.empty()))
+						.distinct() // relies on KeyValue.equals
+						.collect(Collectors.toList()));
 	}
 
 	@Override
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Result.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Result.java
index d04272d52..f98bcec93 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Result.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Result.java
@@ -223,6 +223,10 @@ public class Result extends OafEntity implements Serializable {
     public void mergeFrom(OafEntity e) {
         super.mergeFrom(e);
 
+        if (!Result.class.isAssignableFrom(e.getClass())){
+            return;
+        }
+
         Result r = (Result) e;
 
         instance = mergeLists(instance, r.getInstance());
diff --git a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Software.java b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Software.java
index 655ea1665..6b51a6ada 100644
--- a/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Software.java
+++ b/dhp-schemas/src/main/java/eu/dnetlib/dhp/schema/oaf/Software.java
@@ -49,6 +49,11 @@ public class Software extends Result implements Serializable {
     @Override
     public void mergeFrom(OafEntity e) {
         super.mergeFrom(e);
+
+        if (!Software.class.isAssignableFrom(e.getClass())){
+            return;
+        }
+
         final Software s = (Software) e;
         documentationUrl = mergeLists(documentationUrl, s.getDocumentationUrl());