TYPO3 Core

I added a new frame_class option called 'container'.
Then I have overridden the standard option for the frame_class and space_before_class / space_after_class fields in my_ext/Configuration/TCA/Overrides/tt_content.php like:

$GLOBALS['TCA']['tt_content']['types']['textmedia']['columnsOverrides']['frame_class']['config']['default'] = 'container';

$GLOBALS['TCA']['tt_content']['types']['textmedia']['columnsOverrides']['space_before_class']['config']['default'] = 'medium';
$GLOBALS['TCA']['tt_content']['types']['textmedia']['columnsOverrides']['space_after_class']['config']['default'] = 'medium';

So, if I create a new Text&Media content element, the default values for
frame_class would be container and
space_before_class = medium and space_after_class = medium

I can then change the option in the frame_class back to Standard or any other value that's available in the dropdown.

The same can't be done in the space_before/after_class fields.
If I choose the Standard option the value jumps back to medium. So, selecting the Standard option (which would mean zero space) is not possible anymore.

To solve this, I changed the TCA config for space_before_class / space_after_class in public/typo3/sysext/frontend/Configuration/TCA/tt_content.php to

'space_before_class' => [
            'exclude' => true,
            'label' => 'LLL:EXT:frontend/Resources/Private/Language/locallang_ttc.xlf:space_before_class',
            'config' => [
                'type' => 'select',
                'renderType' => 'selectSingle',
                'items' => [
                    ['LLL:EXT:core/Resources/Private/Language/locallang_general.xlf:LGL.default_value', 'default' ],
                    .....
                ],
                'default' => 'default'
            ]
        ],

After changing the empty value to a string, I can now select the default value in the space_after/before_class field again.
It seems that the problem is the empty value...?

Because the Standard option has "no space" at all, I would suggest to rename the Standard option to "Kein Abstand" with the value "none".
I assume that would solve the problem.

Or add default as value to the Standard option...