diff --git a/dhp-workflows/dhp-aggregation/src/main/java/eu/dnetlib/dhp/migration/AbstractMigrationExecutor.java b/dhp-workflows/dhp-aggregation/src/main/java/eu/dnetlib/dhp/migration/AbstractMigrationExecutor.java
index 3367399c62..11c1fb6aea 100644
--- a/dhp-workflows/dhp-aggregation/src/main/java/eu/dnetlib/dhp/migration/AbstractMigrationExecutor.java
+++ b/dhp-workflows/dhp-aggregation/src/main/java/eu/dnetlib/dhp/migration/AbstractMigrationExecutor.java
@@ -6,6 +6,7 @@ import java.net.URI;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Objects;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.stream.Collectors;
 
@@ -15,7 +16,6 @@ import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
-import org.apache.hadoop.io.IntWritable;
 import org.apache.hadoop.io.SequenceFile;
 import org.apache.hadoop.io.Text;
 import org.codehaus.jackson.map.ObjectMapper;
@@ -36,7 +36,7 @@ public class AbstractMigrationExecutor implements Closeable {
 
 	private final AtomicInteger counter = new AtomicInteger(0);
 
-	private final IntWritable key = new IntWritable(counter.get());
+	private final Text key = new Text();
 
 	private final Text value = new Text();
 
@@ -51,7 +51,7 @@ public class AbstractMigrationExecutor implements Closeable {
 		log.info(String.format("Creating SequenceFile Writer, hdfsPath=%s, nameNode=%s, user=%s", hdfsPath, hdfsNameNode, hdfsUser));
 
 		this.writer = SequenceFile.createWriter(getConf(hdfsNameNode, hdfsUser), SequenceFile.Writer.file(new Path(hdfsPath)), SequenceFile.Writer
-				.keyClass(IntWritable.class), SequenceFile.Writer.valueClass(Text.class));
+				.keyClass(Text.class), SequenceFile.Writer.valueClass(Text.class));
 	}
 
 	private Configuration getConf(final String hdfsNameNode, final String hdfsUser) throws IOException {
@@ -67,7 +67,7 @@ public class AbstractMigrationExecutor implements Closeable {
 
 	protected void emitOaf(final Oaf oaf) {
 		try {
-			key.set(counter.getAndIncrement());
+			key.set(counter.getAndIncrement() + ":" + oaf.getClass().getSimpleName().toLowerCase());
 			value.set(objectMapper.writeValueAsString(oaf));
 			writer.append(key, value);
 		} catch (final Exception e) {
@@ -99,6 +99,8 @@ public class AbstractMigrationExecutor implements Closeable {
 	}
 
 	public static <T> Field<T> field(final T value, final DataInfo info) {
+		if (value == null || StringUtils.isBlank(value.toString())) { return null; }
+
 		final Field<T> field = new Field<>();
 		field.setValue(value);
 		field.setDataInfo(info);
@@ -106,7 +108,7 @@ public class AbstractMigrationExecutor implements Closeable {
 	}
 
 	public static List<Field<String>> listFields(final DataInfo info, final String... values) {
-		return Arrays.stream(values).map(v -> field(v, info)).collect(Collectors.toList());
+		return Arrays.stream(values).map(v -> field(v, info)).filter(Objects::nonNull).collect(Collectors.toList());
 	}
 
 	public static Qualifier qualifier(final String classid, final String classname, final String schemeid, final String schemename) {
@@ -124,10 +126,12 @@ public class AbstractMigrationExecutor implements Closeable {
 			final String schemeid,
 			final String schemename,
 			final DataInfo dataInfo) {
+
 		return structuredProperty(value, qualifier(classid, classname, schemeid, schemename), dataInfo);
 	}
 
 	public static StructuredProperty structuredProperty(final String value, final Qualifier qualifier, final DataInfo dataInfo) {
+		if (value == null) { return null; }
 		final StructuredProperty sp = new StructuredProperty();
 		sp.setValue(value);
 		sp.setQualifier(qualifier);
@@ -178,20 +182,25 @@ public class AbstractMigrationExecutor implements Closeable {
 			final String conferenceplace,
 			final String conferencedate,
 			final DataInfo dataInfo) {
-		final Journal j = new Journal();
-		j.setName(name);
-		j.setIssnPrinted(issnPrinted);
-		j.setIssnOnline(issnOnline);
-		j.setIssnLinking(issnLinking);
-		j.setEp(ep);
-		j.setIss(iss);
-		j.setSp(sp);
-		j.setVol(vol);
-		j.setEdition(edition);
-		j.setConferenceplace(conferenceplace);
-		j.setConferencedate(conferencedate);
-		j.setDataInfo(dataInfo);
-		return j;
+
+		if (StringUtils.isNotBlank(name) || StringUtils.isNotBlank(issnPrinted) || StringUtils.isNotBlank(issnOnline) || StringUtils.isNotBlank(issnLinking)) {
+			final Journal j = new Journal();
+			j.setName(name);
+			j.setIssnPrinted(issnPrinted);
+			j.setIssnOnline(issnOnline);
+			j.setIssnLinking(issnLinking);
+			j.setEp(ep);
+			j.setIss(iss);
+			j.setSp(sp);
+			j.setVol(vol);
+			j.setEdition(edition);
+			j.setConferenceplace(conferenceplace);
+			j.setConferencedate(conferencedate);
+			j.setDataInfo(dataInfo);
+			return j;
+		} else {
+			return null;
+		}
 	}
 
 	public static DataInfo dataInfo(final Boolean deletedbyinference,