@Override
 public long nextValue() throws IOException {
   assertThread("Sorted numeric doc values", creationThread);
   assert valueUpto < in.docValueCount()
       : "valueUpto=" + valueUpto + " in.docValueCount()=" + in.docValueCount();
   valueUpto++;
   return in.nextValue();
 }
 @Override
 public int docValueCount() {
   assertThread("Sorted numeric doc values", creationThread);
   assert in.docValueCount() > 0;
   return in.docValueCount();
 }