Steps to reproduce the issue

Installing Blog Sample Data fails on 5.0-dev after PR #38650 has been merged when error reporting is set to Maximum and PHP 8.1+ is used.

When error reporting is not set to Maximum, the installation succeeds.

But in both cases you get the PHP warnings mentioned below.

See also #38650 (comment) .

Expected result

No PHP warnings, installation of Blog Sample Data succeeds in any case.

Actual result

PHP warnings:

PHP Warning:  Undefined array key "searchindex" in /administrator/components/com_fields/src/Model/FieldModel.php on line 119
PHP Warning:  Attempt to read property "params" on null in /administrator/components/com_fields/src/Model/FieldModel.php on line 120
PHP Warning:  Trying to access array offset on value of type null in /administrator/components/com_fields/src/Model/FieldModel.php on line 120
PHP Warning:  Undefined array key "searchindex" in/administrator/components/com_fields/src/Model/FieldModel.php on line 120
PHP Warning:  Undefined array key "searchindex" in /administrator/components/com_fields/src/Model/FieldModel.php on line 121

System information (as much as possible)

Current 5.0-dev branch with PR #38650 merged.
PHP 8.1

Additional comments

It needs to add isset checks to the if conditions, i.e. change the code here
https://github.com/joomla/joomla-cms/blob/5.0-dev/administrator/components/com_fields/src/Model/FieldModel.php#L118-L124
from

        if (
            (is_null($field) && $data['params']['searchindex'] > 0)
            || ($field->params['searchindex'] != $data['params']['searchindex'])
            || ($data['params']['searchindex'] > 0 && ($field->state != $data['state'] || $field->access != $data['access']))
        ) {
            Factory::getApplication()->enqueueMessage(Text::_('COM_FIELDS_SEARCHINDEX_MIGHT_REQUIRE_REINDEXING'), 'notice');
        }

to

        if (isset($data['params']['searchindex'])
            && ((is_null($field) && $data['params']['searchindex'] > 0)
                || ($field->params['searchindex'] != $data['params']['searchindex'])
                || ($data['params']['searchindex'] > 0 && ($field->state != $data['state'] || $field->access != $data['access'])))
        ) {
            Factory::getApplication()->enqueueMessage(Text::_('COM_FIELDS_SEARCHINDEX_MIGHT_REQUIRE_REINDEXING'), 'notice');
        }

But maybe that's not right, and the right fix would be to add the new parameter searchindex to the fields creating in the blog sample data plugin.