ScrollService return `io.EOF` error when no hits in the response.

Please use the following questions as a guideline to help me answer your issue/question without further inquiry. Thank you.

Which version of Elastic are you using?

[ ] elastic.v7 (for Elasticsearch 7.x) [ ] elastic.v6 (for Elasticsearch 6.x) [x] elastic.v5 (for Elasticsearch 5.x) [ ] elastic.v3 (for Elasticsearch 2.x) [ ] elastic.v2 (for Elasticsearch 1.x)

Please describe the expected behavior

When a scrollService response with no hits in the result, it will return io.EOF error. It make no sense no hits is a EOF error and I don't think it is an error either.

I think the driver should return the response without any error when hits is an empty array.

When I turn on the traceLog, the es server response status is 200.

POST /soa_org_member/member/_search?scroll=5m&size=100 HTTP/1.1
Host: HIDDEN_HOSTNAME:9200
User-Agent: elastic/5.0.79 (darwin-amd64)
Transfer-Encoding: chunked
Accept: application/json
Authorization: Basic HIDDEN
Content-Type: application/json
Accept-Encoding: gzip

*** hidden POST BODY ***

HTTP/1.1 200 OK
Content-Type: application/json; charset=UTF-8

{"_scroll_id":"HIDDEN SCROLL ID","took":94,"timed_out":false,"_shards":{"total":5,"successful":5,"skipped":0,"failed":0},"hits":{"total":0,"max_score":null,"hits":[]}}

Please describe the actual behavior

I found this line of code here related: https://github.com/olivere/elastic/blob/29ee98974cf1984dfecf53ef772d721fb97cb0b9/scroll.go#L438-L440

olivere / elastic