added comment for creator/contributor

dnet-ariadneplus-graphdb-publisher/src/main/java/eu/dnetlib/ariadneplus/elasticsearch/BulkUpload.java

@@ -89,6 +89,7 @@ public class BulkUpload {
                 if (uniqueIsPartOf != null) {
                     ace.setIsPartOf(Arrays.asList(uniqueIsPartOf));
                 }
+                //See https://support.d4science.org/issues/19481#note-1
                 if (ace.getContributor() != null) {
                     ace.getContributor().clear();
                     ace.setContributor(ace.getCreator());