GC 3.0.4: callbackReadField not functional if DB field is null?


I try to use callbackReadField for view form, but
if underlying DB-field (“data”) is null
nothing happens: it is no data in “data”-field displayed and it’s no log-entry for it too:

$crud->callbackReadField('data', function ($value, $row) {
            log_message('debug', 'callback read');
            return 'XXXXXXXXXXXX';

The “callbackColumn”-method works as expected in lists independent of DB value.

How to fix it?
(GC 3.0.4 with Codeigniter 4.3.4)