Lucene40's DocValues (sometimes?) have a bogus extra ordinal

      if (seenOrds.cardinality() != sortedValues.getValueCount()) {
        // TODO: find the bug here and figure out a workaround (we can implement in LUCENE-4547's back compat layer maybe)
        // basically ord 0 is unused by any docs: so the sortedbytes ords are all off-by-one
        // does it always happen? e.g. maybe only if there are missing values? or a bug in its merge optimizations?
        // throw new RuntimeException("dv for field: " + fieldName + " has holes in its ords, valueCount=" + sortedValues.getValueCount() + " but only used: " + seenOrds.cardinality());
      }