/** Collect documents from a bitset. */
private List<Document> collectDocuments(List<Document> l, BitSet bitset) {
if (l == null) {
l = Lists.newArrayListWithCapacity((int) bitset.cardinality());
}
final BitSetIterator i = bitset.iterator();
for (int d = i.nextSetBit(); d >= 0; d = i.nextSetBit()) {
l.add(documents.get(d));
}
return l;
}
