Cannot convert String into Integer

Elastic Stack Logstash
3 
Please see below filter clause in config file,

filter {
    grok {
        match => [ "message", "%{TIMESTAMP_ISO8601:logTimestampString} \[%{WORD:logMode}\]: Server %{WORD:messageType}:%{GREEDYDATA:jsonObject}"]
    }
    json {
        source => "jsonObject"
        target => "doc"
    }
    if ([messageType] == "Request") {
        date {
            locale => "en"
            match => ["logTimestampString", "YYYY-MM-dd HH:mm:ss"]
            target => "requestLogTimestamp"
        }
        mutate {
            add_field => {
                "requestType" => "%{[doc][requestType]}"
            }
        }
    }
    else if ([messageType] == "Response"){
        date {
            locale => "en"
            match => ["logTimestampString", "YYYY-MM-dd HH:mm:ss"]
            target => "responseLogTimestamp"
        }
        if ([doc][message] != "success") {
            mutate {
                add_field => {
                    "ErrorMessage" => "%{[doc][reply][ErrorMessage]}"
                }
            }
        }
        mutate  {
            add_field => {
                "messageStatus" => "%{[doc][message]}"
            }
        }
    }
    mutate {
        add_field => {
                "requestID" => "%{[doc][requestID]}"
        }
        remove_field => [ "jsonObject", "doc", "path", "logTimestampString", "reply", "request", "message"]
    }
}