case LIST:
ListObjectInspector fromLoi = (ListObjectInspector) fromOi;
List<?> fromList = fromLoi.getList(from);
SettableListObjectInspector toLoi = (SettableListObjectInspector) toOi;
to = toLoi.create(fromList.size()); // do not reuse
for (int i = 0; i < fromList.size(); i++) {
Object converted = convert(fromList.get(i),
fromLoi.getListElementObjectInspector(),
toLoi.getListElementObjectInspector());
toLoi.set(to, i, converted);