NullPointerException in Elasticsearch when adding Index Pattern in kibana

[marekmarkowski84]

Elasticsearch version: Version: 7.2.0
Kibana version: 7.2.0
JVM version: JVM: 1.8.0_171
OS version: Ubuntu 18.04

Description of the problem including expected versus actual behavior:
Hey,

I noticed NullPointerException in the Elasticsearch logs (org.elasticsearch.action.fieldcaps.TransportFieldCapabilitiesIndexAction:106) when trying to add in kibana index pattern.
In addition, Kibana does not see the index fields (only meta fields).

I suspect that the reason for the problems is using index_prefixes.

Steps to reproduce:

1. Just delete index if exists

curl -XDELETE "http://localhost:9200/test02"

2. Create index

curl -XPUT "http://localhost:9200/test02" -H 'Content-Type: application/json' -d'{
  "mappings": {
    "properties": {
      "app_name": {
        "type": "text",
        "fields": {
          "keyword": {
            "type": "keyword",
            "ignore_above": 256
          },
          "prefix_app_name": {
            "type": "text",
            "index_prefixes": {
              "min_chars": 1,
              "max_chars": 19
            }
          }
        }
      }
    }
  }
}'

3. Index document

curl -XPOST "http://localhost:9200/test02/_doc" -H 'Content-Type: application/json' -d'{  "app_name":"my super app1"}'

4. Create index pattern in kibana for test02

Exception is thrown after click Next Step

I kibana presents only meta fields

Logs:

[2019-06-28T09:57:12,064][DEBUG][o.e.a.f.TransportFieldCapabilitiesIndexAction] [marekm] null: failed to execute [org.elasticsearch.action.fieldcaps.FieldCapabilitiesIndexRequest@30bb56e3]
org.elasticsearch.transport.RemoteTransportException: [marekm][127.0.0.1:9300][indices:data/read/field_caps[index][s]]
Caused by: java.lang.NullPointerException
	at org.elasticsearch.action.fieldcaps.TransportFieldCapabilitiesIndexAction.shardOperation(TransportFieldCapabilitiesIndexAction.java:106) ~[elasticsearch-7.2.0.jar:7.2.0]
	at org.elasticsearch.action.fieldcaps.TransportFieldCapabilitiesIndexAction.shardOperation(TransportFieldCapabilitiesIndexAction.java:46) ~[elasticsearch-7.2.0.jar:7.2.0]
	at org.elasticsearch.action.support.single.shard.TransportSingleShardAction$1.doRun(TransportSingleShardAction.java:113) ~[elasticsearch-7.2.0.jar:7.2.0]
	at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:758) [elasticsearch-7.2.0.jar:7.2.0]
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) [elasticsearch-7.2.0.jar:7.2.0]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_171]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_171]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_171]

[elasticmachine]

Pinging @elastic/es-search

[viewable]

@jimczi @markharwood
This appears to also be an issue on 6.8.x. Is there any chance of the patch for this being backported to 6.8.x?