logstash 截取kafka 中的json中为空值的 不要这一个字段能做到么？

比如trace_id下面有一个"":""这样传入ES会报错（java.lang.IllegalArgumentException: field name cannot be an empty string）
 {
    "log_time":"2018-08-24 14:03:25.841",
    "logger":"com.netflix.discovery.shared.resolver.aws.ConfigClusterResolver",
    "thread":"AsyncResolver-bootstrap-executor-0",
    "level":"INFO",
    "appname":"testadderapi",
    "message":"Resolving eureka endpoints via configuration",
    "hostname":"appledeMacBook-Air.local",
    "span_id":"",
    "trace_id":"",
    "":"",
    "caller":{
        "class":"com.netflix.discovery.shared.resolver.aws.ConfigClusterResolver",
        "method":"getClusterEndpoints",
        "file":"ConfigClusterResolver.java",
        "line":43
    }
}