# "name cannot be empty string" error if field name starts with
**URL:** https://discuss.elastic.co/t/name-cannot-be-empty-string-error-if-field-name-starts-with/66808
**Category:** Elasticsearch
**Created:** [November 22, 2016, 2:27am UTC](https://discuss.elastic.co/t/name-cannot-be-empty-string-error-if-field-name-starts-with/66808 "2016-11-22T02:27:41Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@wyukawa](https://discuss.elastic.co/u/wyukawa)
#### Post date: [November 22, 2016, 2:27am UTC](https://discuss.elastic.co/t/name-cannot-be-empty-string-error-if-field-name-starts-with/66808/1 "2016-11-22T02:27:41Z")
Although Elasticsearch 5 allows dots-in-field-names, the following error occured.
Is this spec or bug?
```
# curl -XPUT 'localhost:9200/twitter/tweet/1?pretty' -d'
> {
> ".a" : "a"
> }
> '
{
"error" : {
"root_cause" : [
{
"type" : "mapper_parsing_exception",
"reason" : "failed to parse"
}
],
"type" : "mapper_parsing_exception",
"reason" : "failed to parse",
"caused_by" : {
"type" : "illegal_argument_exception",
"reason" : "name cannot be empty string"
}
},
"status" : 400
}
```
\*Elasticsearch version
5.0.1
\*JVM version
1.8.0\_102
\*OS version
CentOS 7.2
---
### Author:  [@mainec](https://discuss.elastic.co/u/mainec)
#### Post date: [November 22, 2016, 11:10am UTC](https://discuss.elastic.co/t/name-cannot-be-empty-string-error-if-field-name-starts-with/66808/2 "2016-11-22T11:10:46Z")
From the discussion here:
>
This looks like a side-effect of how dots in field names were implemented.
What's your exact use-case that's causing this issue?
---
### Author:  [@wyukawa](https://discuss.elastic.co/u/wyukawa)
#### Post date: [November 22, 2016, 3:32pm UTC](https://discuss.elastic.co/t/name-cannot-be-empty-string-error-if-field-name-starts-with/66808/3 "2016-11-22T15:32:39Z")
In my use-case, our users freely send logs through fluentd.
So, this problem occurs.
But, I think that users can change field name.
---
### Author:  [@nik9000](https://discuss.elastic.co/u/nik9000)
#### Post date: [November 22, 2016, 3:49pm UTC](https://discuss.elastic.co/t/name-cannot-be-empty-string-error-if-field-name-starts-with/66808/4 "2016-11-22T15:49:36Z")
> [@wyukawa](#):
>
> In my use-case, our users freely send logs through fluentd.
This is slightly dangerous as a use case, I think.
Elasticsearch is generally fine with having lots of fields. Some features, like doc\_values don't do well with sparse fields. If you disable doc\_values on most fields (so no aggregation or sorting on them) then you are generally ok with sparse fields. But each field does have a non-trivial overhead. And adding new fields on the fly requests a cluster state update which can be time consuming. Having thousands of fields in an index doesn't tend to work well.
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [December 20, 2016, 3:49pm UTC](https://discuss.elastic.co/t/name-cannot-be-empty-string-error-if-field-name-starts-with/66808/5 "2016-12-20T15:49:35Z")
This topic was automatically closed 28 days after the last reply. New replies are no longer allowed.