# Invalid FieldReference issue in logstash
**URL:** https://discuss.elastic.co/t/invalid-fieldreference-issue-in-logstash/194742
**Category:** Logstash
**Created:** [August 11, 2019, 10:49am UTC](https://discuss.elastic.co/t/invalid-fieldreference-issue-in-logstash/194742 "2019-08-11T10:49:08Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@sukku77](https://discuss.elastic.co/u/sukku77)
#### Post date: [August 11, 2019, 10:49am UTC](https://discuss.elastic.co/t/invalid-fieldreference-issue-in-logstash/194742/1 "2019-08-11T10:49:08Z")
Hi All,
I am getting the below logstash exception stack trace after migrated from 6.5.4 to 7.3.0.
Does this mean Logstash is dropping out some events? Do I need to update any template to suppress these warnings. There is no other error trace other than the below warning. Can someone please advice on this. Thanks in advance
```
[2019-08-11T10:02:09,886][WARN][logstash.filters.kv] Exception while parsing KV {:exception=>"Invalid FieldReference: `Actor[akka`"}
```
Regards
Sukumar C
---
### Author:  [@Badger](https://discuss.elastic.co/u/Badger)
#### Post date: [August 11, 2019, 12:34pm UTC](https://discuss.elastic.co/t/invalid-fieldreference-issue-in-logstash/194742/2 "2019-08-11T12:34:36Z")
The kv filter adds fields to the event using [event.set](https://github.com/logstash-plugins/logstash-filter-kv/blob/46cfc5001a44ef4676943696e7fa389a8627cbdb/lib/logstash/filters/kv.rb#L429), which means the field name goes through "[sprintf](https://www.elastic.co/guide/en/logstash/current/event-dependent-configuration.html#sprintf)" processing. That in turn means that things like
```
{ "bar": "[foo][0]=a [foo][1]=[foo][0] [foo][2]=c"}
```
get parsed into
```
"foo" => {
"1" => "[foo][0]",
"0" => "a",
"2" => "c"
},
```
but it also means that the field name cannot contain unmatched square brackets.
A workaround would be to use mutate+gsub to change square bracket to some other character. You would need to use a ruby filter if you want to change the field name back after the kv filter.
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [September 8, 2019, 12:34pm UTC](https://discuss.elastic.co/t/invalid-fieldreference-issue-in-logstash/194742/3 "2019-09-08T12:34:48Z")
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