Bamboo REST API /plan/{projectKey}-{buildKey}/variables POST fails with json content type

Issue Summary

This is reproducible on Data Center:

When modifying Plan variables via the REST API https://docs.atlassian.com/atlassian-bamboo/REST/8.2.4/#d2e5901, Bamboo fails to create new variables when using a JSON content type reporting an HTTP 400 - "You must enter a valid variable name" error

Steps to Reproduce

$ curl -u admin:admin -X GET "https://bamboo.mydomain.net/rest/api/latest/plan/ABC-DFG/variables"
[]

$ curl -H "Content-Type: application/json" -u admin:admin -X POST "https://bamboo.mydomain.net/rest/api/latest/plan/ABC-DFG/variables" -d '{ "name":"foo", "value":"var" }'
You must enter a valid variable name

Expected Results

The variables should be added to the Plan

Actual Results

The request fails with "You must enter a valid variable name"

Workaround

Use the following format:

• /plan/{projectKey}-{buildKey}/variables?name=foo&value=bar
  POST

  $ curl -H "Content-Type: application/x-www-form-urlencoded" -u admin:admin -X POST "https://bamboo.mydomain.net/rest/api/latest/plan/ABC-DFG/variables?name=foo&value=var"
  <?xml version="1.0" encoding="UTF-8" standalone="yes"?><variable name="foo" value="var"/>

  GET

  $ curl -u admin:admin -X GET "https://bamboo.mydomain.net/rest/api/latest/plan/ABC-DFG/variables"
  [{"name":"foo","value":"var"}]