diff --git a/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java b/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java
index 18ce2d9..00d97ec 100644
--- a/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java
+++ b/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java
@@ -26,7 +26,7 @@ import eu.dnetlib.dhp.schema.oaf.*;
 public class ModelSupport {
 
 	/** Defines the mapping between the actual entity type and the main entity type */
-	private static Map<EntityType, MainEntityType> entityMapping = Maps.newHashMap();
+	private static final Map<EntityType, MainEntityType> entityMapping = Maps.newHashMap();
 
 	static {
 		entityMapping.put(EntityType.publication, MainEntityType.result);
diff --git a/src/main/java/eu/dnetlib/dhp/schema/dump/oaf/community/Context.java b/src/main/java/eu/dnetlib/dhp/schema/dump/oaf/community/Context.java
index 3ad692b..16d5a6e 100644
--- a/src/main/java/eu/dnetlib/dhp/schema/dump/oaf/community/Context.java
+++ b/src/main/java/eu/dnetlib/dhp/schema/dump/oaf/community/Context.java
@@ -32,7 +32,7 @@ public class Context extends Qualifier {
 
 	@Override
 	public int hashCode() {
-		String provenance = new String();
+		String provenance = "";
 		this.provenance.forEach(p -> provenance.concat(p.toString()));
 		return Objects.hash(getCode(), getLabel(), provenance);
 	}
diff --git a/src/main/java/eu/dnetlib/dhp/schema/oaf/AccessRight.java b/src/main/java/eu/dnetlib/dhp/schema/oaf/AccessRight.java
index 47de365..14fe748 100644
--- a/src/main/java/eu/dnetlib/dhp/schema/oaf/AccessRight.java
+++ b/src/main/java/eu/dnetlib/dhp/schema/oaf/AccessRight.java
@@ -22,7 +22,7 @@ public class AccessRight extends Qualifier {
 		String s = super.toComparableString();
 		return Optional
 			.ofNullable(getOpenAccessRoute())
-			.map(x -> s + "::" + x.toString())
+			.map(x -> s + "::" + x)
 			.orElse(s);
 	}
 
diff --git a/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/CleaningFunctions.java b/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/CleaningFunctions.java
index 43f3500..56ee75a 100644
--- a/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/CleaningFunctions.java
+++ b/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/CleaningFunctions.java
@@ -37,10 +37,7 @@ public class CleaningFunctions {
 		if (CleaningFunctions.PID_BLACKLIST.contains(pidValue)) {
 			return false;
 		}
-		if (PidBlacklistProvider.getBlacklist(s.getQualifier().getClassid()).contains(pidValue)) {
-			return false;
-		}
-		return true;
+		return !PidBlacklistProvider.getBlacklist(s.getQualifier().getClassid()).contains(pidValue);
 	}
 
 	/**
diff --git a/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidComparator.java b/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidComparator.java
index 2bee0eb..a2bc65a 100644
--- a/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidComparator.java
+++ b/src/main/java/eu/dnetlib/dhp/schema/oaf/utils/PidComparator.java
@@ -11,7 +11,7 @@ import eu.dnetlib.dhp.schema.oaf.StructuredProperty;
 
 public class PidComparator<T extends OafEntity> implements Comparator<StructuredProperty> {
 
-	private T entity;
+	private final T entity;
 
 	public PidComparator(T entity) {
 		this.entity = entity;
diff --git a/src/test/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactoryTest.java b/src/test/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactoryTest.java
index 215d834..9ef50dd 100644
--- a/src/test/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactoryTest.java
+++ b/src/test/java/eu/dnetlib/dhp/schema/oaf/utils/IdentifierFactoryTest.java
@@ -16,7 +16,7 @@ import eu.dnetlib.dhp.schema.oaf.Publication;
 
 public class IdentifierFactoryTest {
 
-	private static ObjectMapper OBJECT_MAPPER = new ObjectMapper()
+	private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper()
 		.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
 
 	@Test