Simulate API returning an error in version 6.4.1

[melvynator]

The version 6.4.1 seem to have a problem with the simulate API:

PUT _ingest/pipeline/per_dat_loc_recognition
{
  "description": "A pipeline to do dates, locations and persons recognition",
  "processors": [
    {
      "opennlp" : {
        "field" : "original"
      }
    }
  ]
}


POST _ingest/pipeline/per_dat_loc_recognition/_simulate
{
  "docs": [
    {
      "_source": {
        "original" : "John Smith has been working in New York since September 2015"
      }
    }
  ]
}

This return the following error:

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "unexpected value type [class java.util.HashSet]"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "unexpected value type [class java.util.HashSet]"
  },
  "status": 400
}

But the following work perfectly fine:

PUT ingest_pipeline_index/_doc/1?pipeline=per_dat_loc_recognition
{
  "original" : "John Smith has been working in New York since September 2015"
}

GET ingest_pipeline_index/_search

Give the result:

{
  "took": 0,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 1,
    "max_score": 1,
    "hits": [
      {
        "_index": "ingest_pipeline_index",
        "_type": "_doc",
        "_id": "1",
        "_score": 1,
        "_source": {
          "original": "John Smith has been working in New York since September 2015",
          "entities": {
            "persons": [
              "John Smith"
            ],
            "dates": [
              "since September 2015"
            ],
            "locations": [
              "New York"
            ]
          }
        }
      }
    ]
  }
}