Highlighting _all does not work with Elastic Seach

Output.txt

Starting test
{"ok":true,"_index":"test","_type":"dossier","_id":"1","_version":19}
{"ok":true,"_index":"test","_type":"dossier","_id":"2","_version":13}
{
  "took" : 6,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  },
  "hits" : {
    "total" : 2,
    "max_score" : 1.0,
    "hits" : [ {
      "_index" : "test",
      "_type" : "dossier",
      "_id" : "1",
      "_score" : 1.0, "_source" : { "conformite":"CONFORME", "direction":"DIRECTION"},
      "highlight" : {
        "conformite" : [ "<em>CONFORME</em>" ]
      }
    }, {
      "_index" : "test",
      "_type" : "dossier",
      "_id" : "2",
      "_score" : 1.0, "_source" : { "conformite":"NONCONFORME", "direction":"BRETAGNE"},
      "highlight" : {
        "conformite" : [ "<em>NONCONFORME</em>" ]
      }
    } ]
  }
}
{
  "took" : 5,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  },
  "hits" : {
    "total" : 2,
    "max_score" : 1.0,
    "hits" : [ {
      "_index" : "test",
      "_type" : "dossier",
      "_id" : "1",
      "_score" : 1.0, "_source" : { "conformite":"CONFORME", "direction":"DIRECTION"}
    }, {
      "_index" : "test",
      "_type" : "dossier",
      "_id" : "2",
      "_score" : 1.0, "_source" : { "conformite":"NONCONFORME", "direction":"BRETAGNE"}
    } ]
  }
}

testHighlight.sh

echo 'Starting test'
curl -XPUT http://localhost:9200/test/dossier/1 -d '{ "conformite":"CONFORME", "direction":"DIRECTION"}'
echo ''
curl -XPUT http://localhost:9200/test/dossier/2 -d '{ "conformite":"NONCONFORME", "direction":"BRETAGNE"}'
echo ''
curl -XGET http://localhost:9200/test/_search?pretty=true -d '{
"query" : {
  "wildcard" : {
    "conformite" : "*"
    }
  },
"highlight" : {
  "fields" : {
    "conformite" : {}
    }
  }
}'
echo ''
curl -XGET http://localhost:9200/test/_search?pretty=true -d '{
"query" : {
  "wildcard" : {
    "conformite" : "*"
    }
  },
"highlight" : {
  "fields" : {
    "_all" : {}
    }
  }
}'
echo ''