Issue Summary

Once you set a value for a Text Field single-line (custom field) and then clear that value, Jira's JQL will not recognize that field as EMPTY anymore.

Steps to Reproduce

1. Create an issue with a custom field (single-line text field)
2. remove the custom field value later
3. Make a JQL search:

   "singleLineTextFielsName" ~ "fieldvalue"

Expected Results

The field should be considered as empty again since no information is set.

Actual Results

JQL still shows the issue where the field is no more set.
Rest API shows correct data.

Workaround

As a workaround, you can exclude these issues by adding AND custom_field IS NOT EMPTY to your JQL search.

You can also allow Automation for Jira to properly clear this field for you by running an automation that updates this field to a "NULL" value. You can import this rule and apply it to your own text field: automation-rule-2616645-202111011333.json

Note: This can also happen with Read only custom fields where similar behaviour can be seen.