Routine Load解析JSON,如果JSON解析字段没有,则为空怎么写?

CREATE ROUTINE LOAD market_new_dw.zhiguan_pre_log2 ON zhiguan_pre_log2 COLUMNS ( hostName, message, prospectorType, beatVersion, tagsSyslog, inputType, inputSource, logFilePath ) PROPERTIES (
“desired_concurrent_number” = “8”,
“format” = “json”,
“jsonpaths” = “[”$.host.name","$.message","$.prospector.type","$.beat.version","$.tags","$.input.type","$.input.source","$.log.file.path"]"
)
FROM
KAFKA ( “kafka_broker_list” = “10.96.9.122:9092”, “kafka_topic” = “zhiguan-filebeat-log”, “kafka_partitions” = “0,1,2,3”, “property.kafka_default_offsets” = “OFFSET_BEGINNING” );
如果$.message 没有key数值,则数值为空,则怎么写?