Expressions don't have nulls, only doubles. If the field is missing, then its treated as 0.0. You can query .empty to see if its missing and substitute something else. See https://github.com/elastic/elasticsearch/pull/18132#discussion_r62068494
* Reorganize scripting documentation * Further changes to tidy up scripting docs Closes #18116 * Add note about .lat/lon potentially returning null * Added .value to expressions example * Fixed two bad ASCIIDOC links
James Rodewig
Robert Muir
Clinton Gormley