Views field handler custom locked status

The custom output option for the "Is Locked" views field handler does not appear to work.

Steps to reproduce

1. Create a new view page that displays content of all types that displays a table of fields
2. Add the "Content Lock: Is Locked" field
3. Choose "custom" in the output format
4. Add "L" in the "Custom output for TRUE" field
5. Add "U" in the "Custom output for FALSE" field
6. Apply to all displays

Expected

The view preview will show a list of nodes and the "Is Locked" column will display "U" or "L"

Actual

The view preview shows a list of nodes and the "Is Locked" column displays "No" and "Yes" which are the default settings.

It looks like the "custom" option is not handled within the render function of views_handler_field_is_locked.inc