ElasticsearchSink2 write json data into es 2.3.3，why have a "body" object under "_source" object？

[mymaoqiu]

write data: { "action_type": "media", "test_double": "2131312312", "media_type": "mobile", "created_timestamp": "2016-09-07 09:42:57", "is_incr": "yes", "browser_lang": "OTHER", "device_mobile": "15559850392", "device_os_ver": "Unknown", "media_code": "bj001", "test_long": 12313123, "browser_ver": "sss", "loc_ip": "61.233.69.82", "device_mac": "00:70:A4:00:00:5C", "browser": "Downloading Tool", "browser_core": "OTHER", "adid": "123126", "device_os": "UNKNOWN", "space_code": "index" }

result in es 2.3.3: { "_index": "portal-ad", "_type": "log22", "_id": "AVdB84VbxE8oIkj-6i9D", "_version": 1, "_score": 1, "_source": { "body": { "action_type": "media", "test_double": "2131312312", "media_type": "mobile", "created_timestamp": "2016-09-07 09:42:57", "is_incr": "yes", "browser_lang": "OTHER", "device_mobile": "15559850392", "device_os_ver": "Unknown", "media_code": "bj001", "test_long": 12313123, "browser_ver": "sss", "loc_ip": "61.233.69.82", "device_mac": "00:70:A4:00:00:5C", "browser": "Downloading Tool", "browser_core": "OTHER", "adid": "123126", "device_os": "UNKNOWN", "space_code": "index" } } }