diff --git a/dhp-workflows/dhp-patch/src/main/java/eu/dnetlib/dhp/patchrefereed/SparkPatchRefereed.java b/dhp-workflows/dhp-patch/src/main/java/eu/dnetlib/dhp/patchrefereed/SparkPatchRefereed.java
index 5390a9f906..2dd0bfe2ca 100644
--- a/dhp-workflows/dhp-patch/src/main/java/eu/dnetlib/dhp/patchrefereed/SparkPatchRefereed.java
+++ b/dhp-workflows/dhp-patch/src/main/java/eu/dnetlib/dhp/patchrefereed/SparkPatchRefereed.java
@@ -153,24 +153,30 @@ public class SparkPatchRefereed implements Serializable {
 		return false;
 	}
 
+	//TODO verify the reason of the NullPointerException fired at line 167
 	private static boolean equals(List<String> url, List<String> url1) {
-		if (url == null && url1 == null) {
-			return true;
-		}
+		try{
+			if (url == null && url1 == null) {
+				return true;
+			}
 
-		if ((url1 == null && url != null) || (url != null && url1 == null)) {
-			return false;
-		}
-
-		if (url.size() != url1.size()) {
-			return false;
-		}
-		for (String u : url) {
-			if (!url1.contains(u)) {
+			if ((url1 == null && url != null) || (url != null && url1 == null)) {
 				return false;
 			}
+
+			if (url.size() != url1.size()) {
+				return false;
+			}
+			for (String u : url) {
+				if (!url1.contains(u)) {
+					return false;
+				}
+			}
+			return true;
+		}catch(Exception e){
+			return false;
 		}
-		return true;
+
 	}
 
 	public static <R> Dataset<R> readPath(