fixed: https://github.com/ViaQ/fluent-plugin-viaq_data_model/commit/1084c3f85b5d25c4f929ccb055c43fec39d87c9f

Reproduced with v3.9, The message is blank when event is string.
With openshift3/logging-fluentd/images/v3.10.0-0.67.0.0. The string event message are in message field.


{
  "_index": ".operations.2018.06.13",
  "_type": "com.redhat.viaq.common",
  "_id": "MTA3ZjEzYTUtMjFjNC00YzkzLWFmMWItYjI2ZDJiOTU3Y2Vi",
  "_score": null,
  "_source": {
    "event": "anlieventevent",
    "verb": "ADDED",
    "logtag": "F",
    "docker": {
      "container_id": "d3bc9346e4d9f808463536e12a8d752fd5c8cb5e96e29a77a44647a4620df92b"
    },
    "kubernetes": {
      "container_name": "kube-eventrouter",
      "namespace_name": "default",
      "pod_name": "logging-eventrouter-1-pzf8v-debug",
      "pod_id": "39729dbb-6ed2-11e8-9b3b-fa163e8298c1",
      "host": "qe-anli10node-registry-router-2",
      "master_url": "https://kubernetes.default.svc.cluster.local",
      "namespace_id": "95fe5920-6ea3-11e8-96d9-fa163e8298c1"
    },
    "message": "{ \"event\": \"anlieventevent\", \"verb\": \"ADDED\" }",
    "level": "info",
    "hostname": "qe-anli10node-registry-router-2",
    "pipeline_metadata": {
      "collector": {
        "ipaddr4": "10.130.0.14",
        "ipaddr6": "fe80::50ca:88ff:fe1d:dc7",
        "inputname": "fluent-plugin-systemd",
        "name": "fluentd",
        "received_at": "2018-06-13T06:30:39.224634+00:00",
        "version": "0.12.42 1.6.0"
      }
    },
    "@timestamp": "2018-06-13T06:30:39.043046+00:00",
    "viaq_msg_id": "MTA3ZjEzYTUtMjFjNC00YzkzLWFmMWItYjI2ZDJiOTU3Y2Vi"
  },
  "fields": {
    "@timestamp": [
      1528871439043
    ],
    "pipeline_metadata.collector.received_at": [
      1528871439224
    ]
  },
  "highlight": {
    "kubernetes.pod_name": [
      "@kibana-highlighted-field@logging-eventrouter-1-pzf8v-debug@/kibana-highlighted-field@"
    ]
  },
  "sort": [
    1528871439043
  ]
}