null_value

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:

 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" } } } 

1. Replace explicit null values with the term NULL.
2. An empty array does not contain an explicit null, and so won’t be replaced with the null_value.
3. A query for NULL returns document 1, but not document 2.