Problem

JQL supports sorting by the custom field values with the 'ORDER BY' clause:

 project = MyProject ORDER BY MyCustomField

For this to work, Jira built-in custom fields store sorted_cf_name in the Lucene document. Whenever there is a custom field value assigned to an issue, it is stored in the index. However, when no value exists for a custom field, the sorting marker is stored instead (Double.MAX_VALUE, Long.MAX_VALUE or \ufffd depending on the custom field's type).

Solution

As the comparators used by Jira built-in custom fields are capable of sort null values correctly, so we decided not to store markers for null values in the Lucene index any more and rely on comparators to sort null values.

This feature is only available in Jira Data Center 8.10 and later.
See also: Optimizing custom fields