{
  "pipeline" :
  {
    "description": "_description",
    "processors": [
      {
        "rename" : {
          "field" : "{{foo}}",
          "target_field": "bar",
          "ignore_missing": true
        }
      }
    ]
  },
  "docs": [
    {
      "_index": "index",
      "_id": "id",
      "_source": {
        "message": "test"
      }
    }
  ]
}

{
  "docs": [
    {
      "error": {
        "root_cause": [
          {
            "type": "illegal_argument_exception",
            "reason": "path cannot be null nor empty"
          }
        ],
        "type": "illegal_argument_exception",
        "reason": "path cannot be null nor empty"
      }
    }
  ]
}