@Override
 public void collect(int doc) {
   try {
     FieldsVisitor fieldsVisitor = new FieldsVisitor(false);
     context.reader().document(doc, fieldsVisitor);
     Uid uid = fieldsVisitor.uid();
     final long version =
         Versions.loadVersion(context.reader(), new Term(UidFieldMapper.NAME, uid.toBytesRef()));
     docsToPurge.add(new DocToPurge(uid.type(), uid.id(), version, fieldsVisitor.routing()));
   } catch (Exception e) {
     logger.trace("failed to collect doc", e);
   }
 }