java8 使用stream排序空字段排在前面或后面

list.stream().sorted(Comparator.comparing(l -> l.getCreateTime(), Comparator.nullsFirst(Date::compareTo))).collect(toList());
toOrderList.stream().sorted(Comparator.comparing(l -> l.getContractCode(), Comparator.nullsFirst(String::compareTo))).collect(toList());

resultList.stream().sorted(Comparator.comparing(Role::getCreateTime)).collect(Collectors.toList());

resultList.stream().sorted(Comparator.comparing(Role::getCreateTime).reversed()).collect(Collectors.toList());