Cannot send empty request body - empty request body is replaced to empty JSON object

[krzotr]

_forcemerge has changed in 6.4.0 - REST API: Reject forcemerge requests with a body https://github.com/elastic/elasticsearch/pull/30792 (issue: https://github.com/elastic/elasticsearch/issues/29584)

I use Elasticsearch 6.5.1. I try to manually run _forcemerge command on a specified index.

In that case, I go to Any Request tab, put test/_forcemerge?max_num_segments=1 in path field, select POST method, remove whole request body. After I press Request button I see Error 400 with message forcemerge takes arguments in query parameters, not in the request body.

The problem is _forcemerge does not allow to send a request body. Currentl,y empty body of request is replaced with empty JSON object {}), it must be empty!

Please check _forcemerge with curl requests.

Send empty JSON object instead of empty body - error

$ curl -H "Content-Type: application/json" -XPOST "http://192.168.1.27:9200/test/_forcemerge?max_num_segments=1" -d "{}"
{"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"forcemerge takes arguments in query parameters, not in the request body"}],"type":"illegal_argument_exception","reason":"forcemerge takes arguments in query parameters, not in the request body"},"status":400}

Send empty request body - everything is OK

$ curl -H "Content-Type: application/json" -XPOST "http://192.168.1.27:9200/test/_forcemerge?max_num_segments=1" -d ""
{"_shards":{"total":10,"successful":5,"failed":0}}

In my opinion to send empty request body should be checkbox Empty body next to Pretty. When Empty body is selected textarea form should be disabled.