Dashboard Rest UI - Error: Content-Type header

(from github.com/defensivedepth)
Using FESS 12.0 with included ES. When I run a POST request from the Dashboard Rest UI, I get the following error:

{ "error": "Content-Type header [application/x-www-form-urlencoded] is not supported", "status": 406 }

This appears to be related to how ES 6 changes Content-Type checking:

(from github.com/marevol)
Fixed in #1426.

(from github.com/defensivedepth)