字段类型为keyword,但是term聚合不成功

聚合有hits,
但是没有aggregations
执行结果如下:
{
"took": 16,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"skipped": 0,
"failed": 0
},
"hits": {
"total": 4427971,
"max_score": 1,
"hits": [ { "_index": .......
}
}
是社么问题呢?
感谢