Steps to reproduce the issue

1. Have a prefixed table with the checked_out column with NULL not allowed.
2. Have the globalcheckin task enabled and running on a schedule
3. Do some backend admin to checkout an item from this table and leave it checked out for long enough for globalcheckin to be triggered on it.

Expected result

The "item" is checked in by the scheduled task.

Actual result

The task returns error code -2, resulting in task failure email if configured to send emails on failure.

System information (as much as possible)

Joomla 5.3.2
MySQL 8.0.36
GlobalCheckin plugin 5.0.0
PHP 8.3.15

Additional comments

The globalcheckin plugin (version 5.0.0) does not cater properly for tables with "NULL not allowed" in the checked_out column. The code ~/plugins/task/globalcheckin/src/Extension/GlobalCheckin.php caters for both "not NULL" and null allowed in the WHERE clause but tries to set the checked_out column field value to NULL when expired checked out rows are found irrespective of NULL being allowed or not.

Changing the code:

$query = $db->getQuery(true)
    ->update($db->quoteName($tn))
    ->set($db->quoteName('checked_out') . ' = NULL')
    ->set($db->quoteName('checked_out_time') . ' = NULL');

if ($fields['checked_out']->Null === 'YES') {
    $query->where($db->quoteName('checked_out') . ' IS NOT NULL');
} else {
    $query->where($db->quoteName('checked_out') . ' > 0');
}

to:

$query = $db->getQuery(true)
    ->update($db->quoteName($tn))
    ->set($db->quoteName('checked_out_time') . ' = NULL');

if ($fields['checked_out']->Null === 'YES') {
    $query->set($db->quoteName('checked_out') . ' = NULL')               
          ->where($db->quoteName('checked_out') . ' IS NOT NULL');
} else {
    $query->set($db->quoteName('checked_out') . ' = 0')
          ->where($db->quoteName('checked_out') . ' > 0');
}

Fixes the problem