@Override
 public void setNextReader(AtomicReaderContext reader) {
   try {
     bits =
         DocIdSets.toSafeBits(
             reader.reader(), filter.getDocIdSet(reader, reader.reader().getLiveDocs()));
   } catch (IOException ioe) {
     throw new AggregationExecutionException(
         "Failed to aggregate filter aggregator [" + name + "]", ioe);
   }
 }