Empty settings lead to "no settings to update" 400 error

[VeggieMeat]

Original issue: https://www.drupal.org/node/2646006

Problem/Motivation

When sending an empty array to Elasticsearch it becomes very unhappy. Try:

curl -XPUT 'http://localhost:9200/some_existing_index/_settings'

you will get a 400 error.

Proposed resolution

Don't send a nothing.

Remaining tasks

User interface changes

API changes

Data model changes