@Override
 public int hashCode() {
   int result = contributorOrcid != null ? contributorOrcid.hashCode() : 0;
   result = 31 * result + (creditName != null ? creditName.hashCode() : 0);
   result = 31 * result + (contributorEmail != null ? contributorEmail.hashCode() : 0);
   result = 31 * result + (contributorAttributes != null ? contributorAttributes.hashCode() : 0);
   return result;
 }