Get tasks using REST API

[nice]

I need to get tasks using query, for example:

POST     http://1.9.84.51:8080/activiti-rest/service/query/tasks
{
  "includeProcessVariables":"true",
  "assignee": "trump",
  "formKey": "EvaluationForm01"
}

I am getting:  Unrecognized field "formKey"

When I remove "formKey" I can see it in the result!
What am I doing wrong?

[jbarrez]

I'm not sure if the API supports that. The docs don't seem to include that particular property: http://activiti.org/userguide/index.html#_query_for_tasks