@CheckForNull
 private static String computeRevision(@Nullable Changeset latestChange) {
   if (latestChange == null) {
     return null;
   }
   return latestChange.getRevision();
 }
 @CheckForNull
 private static String computeRevision(
     FileSourceDto previousDto, @Nullable Changeset latestChange) {
   if (latestChange == null) {
     return previousDto.getRevision();
   }
   return latestChange.getRevision();
 }