Github user MikeThomsen commented on the issue:
https://github.com/apache/nifi/pull/2501
This isn't easily tested with a unit test, so here's a flowfile that can be
tested against an ES instance running on localhost:9200 (ie defaults)
[Nullable_ES_Test.xml.txt](https://github.com/apache/nifi/files/1771209/Nullable_ES_Test.xml.txt)---
