diff --git a/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/GraphCleaningFunctions.java b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/GraphCleaningFunctions.java
index fdfd63a15..b6574da16 100644
--- a/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/GraphCleaningFunctions.java
+++ b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/GraphCleaningFunctions.java
@@ -810,7 +810,7 @@ public class GraphCleaningFunctions extends CleaningFunctions {
 		return author;
 	}
 
-	private static Optional<String> cleanDateField(Field<String> dateofacceptance) {
+	public static Optional<String> cleanDateField(Field<String> dateofacceptance) {
 		return Optional
 			.ofNullable(dateofacceptance)
 			.map(Field::getValue)
diff --git a/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/MergeUtils.java b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/MergeUtils.java
index 79a12d630..4c411a155 100644
--- a/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/MergeUtils.java
+++ b/dhp-common/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/MergeUtils.java
@@ -654,16 +654,9 @@ public class MergeUtils {
 	}
 
 	private static Field<String> selectOldestDate(Field<String> d1, Field<String> d2) {
-		if (d1 == null || StringUtils.isBlank(d1.getValue())) {
+		if (!GraphCleaningFunctions.cleanDateField(d1).isPresent()) {
 			return d2;
-		} else if (d2 == null || StringUtils.isBlank(d2.getValue())) {
-			return d1;
-		}
-
-		if (StringUtils.contains(d1.getValue(), "null")) {
-			return d2;
-		}
-		if (StringUtils.contains(d2.getValue(), "null")) {
+		} else if (!GraphCleaningFunctions.cleanDateField(d2).isPresent()) {
 			return d1;
 		}
 
@@ -715,7 +708,9 @@ public class MergeUtils {
 	private static String spKeyExtractor(StructuredProperty sp) {
 		return Optional
 			.ofNullable(sp)
-			.map(s -> Joiner.on("||")
+			.map(
+				s -> Joiner
+					.on("||")
 					.useForNull("")
 					.join(qualifierKeyExtractor(s.getQualifier()), s.getValue()))
 			.orElse(null);