/** Rolls up any single-valued hierarchical dimensions. */
protected void rollup() throws IOException {
// Rollup any necessary dims:
for(Map.Entry<String,DimConfig> ent : config.getDimConfigs().entrySet()) {
String dim = ent.getKey();
DimConfig ft = ent.getValue();
if (ft.hierarchical && ft.multiValued == false) {
int dimRootOrd = taxoReader.getOrdinal(new FacetLabel(dim));
// It can be -1 if this field was declared in the
// config but never indexed:
if (dimRootOrd > 0) {