Null and nil

[rojin]

Hello everyone! I have a grok pattern which some of its fields may include "null" values. How am I supposed to show null in kibana? or logstash output? I have defined the pattern as number for those fields.

input {
    file {
	type => "log"
        path => "/home/rojin/Desktop/customer/customer.log"
        start_position => "beginning"
        sincedb_path => "/dev/null"
    }
}

filter {
    if "INFO" in [message] and "successfully" in [message] {
        grok {
            patterns_dir => ["path/to/patterns"]
            match => { "message" => "pattern" }
            remove_field => ["message","@timestamp"]
        }
    } else if "ERROR" in [message]{
       ...
    }


    mutate {
	    convert => {
            "myfield" => "boolean"
            ...
        }
    }
}

output {
      stdout { codec=> rubydebug }
}

I have a "message" field and I use match in grok filter in a conditional format (there are multiple patterns in my log file) to seperate my fields and then I use remove_field for "message". I have tested below solution but got no result. actually it does not parse my message and does not create fields. (_grokparsefailure):

if "PersonId" in [message] and ![PersonId] {
             ruby {
                code => 'event.set("person_ID",nil)'
             }
    }

Can someone please explain help me with this? Thanks in advance!