@Override
 @Nullable
 public Uri getThumbnailUri() {
   if (hasThumbnail) {
     return PartAuthority.getAttachmentThumbnailUri(attachmentId);
   } else {
     return null;
   }
 }
 @Override
 @Nullable
 public Uri getDataUri() {
   if (hasData) {
     return PartAuthority.getAttachmentDataUri(attachmentId);
   } else {
     return null;
   }
 }
 @Override
 @NonNull
 public Uri getThumbnailUri() {
   return PartAuthority.getAttachmentThumbnailUri(attachmentId);
 }
 @Override
 @NonNull
 public Uri getDataUri() {
   return PartAuthority.getAttachmentDataUri(attachmentId);
 }