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:

  1. PUT my-index-000001
  2. {
  3.   "mappings": {
  4.     "properties": {
  5.       "status_code": {
  6.         "type":       "keyword",
  7.         "null_value": "NULL" 
  8.       }
  9.     }
  10.   }
  11. }
  13. PUT my-index-000001/_doc/1
  14. {
  15.   "status_code": null
  16. }
  18. PUT my-index-000001/_doc/2
  19. {
  20.   "status_code": [] 
  21. }
  23. GET my-index-000001/_search
  24. {
  25.   "query": {
  26.     "term": {
  27.       "status_code": "NULL" 
  28.     }
  29.   }
  30. }

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.