How to reproduce zero values for _explanation in elasticsearch.

explain_zero_value.sh

# create index
curl -XPOST "http://localhost:9200/test"

# create mapping with name field boosted
curl -XPOST "http://localhost:9200/test/user/_mapping" -d '{
   "user":{
      "properties":{
         "name":{
            "type":"string",
            "boost": 2.0
         }
      }
   }
}'

# insert test data
curl -XPOST "http://localhost:9200/test/user" -d '{
    "name": "Test User",
    "email": "user@test.org",
    "nickname": "test"
}'

# query index with explain option
curl -XGET "http://localhost:9200/test/user/_search?q=test&explain=&pretty=true"
{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  },
  "hits" : {
    "total" : 1,
    "max_score" : 0.26849622,
    "hits" : [ {
      "_shard" : 2,
      "_node" : "XGJXm_GmTqSxLN3A34TL9w",
      "_index" : "test",
      "_type" : "user",
      "_id" : "Jz6fBN1mRROcp-4qnd-0xQ",
      "_score" : 0.26849622, "_source" : { "name": "Test User", "email": "user@test.org", "nickname": "test" },
      "_explanation" : {
        "value" : 0.0,
        "description" : "btq, product of:",
        "details" : [ {
          "value" : 0.0,
          "description" : "weight(_all:test in 0) [PerFieldSimilarity], result of:",
          "details" : [ {
            "value" : 0.0,
            "description" : "fieldWeight in 0, product of:",
            "details" : [ {
              "value" : 0.0,
              "description" : "tf(freq=0.0), with freq of:",
              "details" : [ {
                "value" : 0.0,
                "description" : "phraseFreq=0.0"
              } ]
            }, {
              "value" : 0.30685282,
              "description" : "idf(docFreq=1, maxDocs=1)"
            }, {
              "value" : 0.4375,
              "description" : "fieldNorm(doc=0)"
            } ]
          } ]
        }, {
          "value" : 2.0,
          "description" : "allPayload(...)"
        } ]
      }
    } ]
  }
}