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Elastic Docs ›Elasticsearch Guide [master] ›Mapping ›Mapping parameters
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null_valueedit

A null value cannot be indexed or searched. When a field is set to null, (or an empty array or an array of null values) it is treated as though that field has no values.

The null_value parameter allows you to replace explicit null values with the specified value so that it can be indexed and searched. For instance:

response = client.indices.create(
  index: 'my-index-000001',
  body: {
    mappings: {
      properties: {
        status_code: {
          type: 'keyword',
          nil_value: 'NULL'
        }
      }
    }
  }
)
puts response

response = client.index(
  index: 'my-index-000001',
  id: 1,
  body: {
    status_code: nil
  }
)
puts response

response = client.index(
  index: 'my-index-000001',
  id: 2,
  body: {
    status_code: []
  }
)
puts response

response = client.search(
  index: 'my-index-000001',
  body: {
    query: {
      term: {
        status_code: 'NULL'
      }
    }
  }
)
puts response
PUT my-index-000001
{
  "mappings": {
    "properties": {
      "status_code": {
        "type":       "keyword",
        "null_value": "NULL" 
      }
    }
  }
}

PUT my-index-000001/_doc/1
{
  "status_code": null
}

PUT my-index-000001/_doc/2
{
  "status_code": [] 
}

GET my-index-000001/_search
{
  "query": {
    "term": {
      "status_code": "NULL" 
    }
  }
}

Replace explicit null values with the term NULL.

An empty array does not contain an explicit null, and so won’t be replaced with the null_value.

A query for NULL returns document 1, but not document 2.

The null_value needs to be the same data type as the field. For instance, a long field cannot have a string null_value.

The null_value only influences how data is indexed, it doesn’t modify the _source document.

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