[Bug] SystemSetting not saving the settings for FieldConfig::TYPE_ARRAY if all options are unselected

[AltamashShaikh]

What happened?

We recently created a new SystemSetting called anonymizeClickIds for AdvertisingConversionExport plugin, below is the code to create the system setting.

$providers = AdvertisingConversionExport::getAvailableClickIdProviders();
        $defaultValues = [];
        $availableValues = [];
        foreach ($providers as $provider) {
            $defaultValues[] = $provider::ID;
            $availableValues[] = ['name' => 'anonymizeClickIds[]', 'value' => $provider->getName(), 'key' => $provider::ID];
        }
$this->makeSetting('anonymizeClickIds', $defaultValues, FieldConfig::TYPE_ARRAY, function (FieldConfig $field) use ($defaultValues, $availableValues) {
            $faqURL = Url::addCampaignParametersToMatomoLink(
                'https://matomo.org/faq/advertising-conversion-export/exported-clickids-have-value-as-anonymized/',
                null,
                null,
                'App.CoreAdminHome.generalSettings'
            );
            $field->introduction = Piwik::translate('AdvertisingConversionExport_AnonymiseClickIDSettingTitle');
            $field->inlineHelp = Piwik::translate(
                'AdvertisingConversionExport_AnonymiseClickIDSettingDescription',
                [
                    '<a target="_blank" rel="noreferrer noopener" href="' . $faqURL . '">',
                    '</a>',
                    '<br><br><strong>',
                    '</strong>',
                ]
            );
            $field->uiControl = FieldConfig::UI_CONTROL_CHECKBOX;
            $field->availableValues = $availableValues;
            $field->validate = function ($values) use ($defaultValues) {
                foreach ($values as $value) {
                    if (!in_array($value, $defaultValues)) {
                        throw new \Exception('Invalid value "' . $value . '"');
                    }
                }
            };
        });

This shows the setting correctly

But there is one error, if you unselect all the options and try to save the setting, the setting shows as saved successfully, but it reverts back to the last saved setting.

What should happen?

We should be able to save the setting, with all the options as unselected.

How can this be reproduced?

1. Activate AdvertisingConversionExport plugin.
2. Got to system settings, under Admin > System >GeneralSettings
3. Scroll down to AdvertisingConversionExport section
4. Unselect all the options for Anonymise Click IDs settings and press save
5. Refresh the page
6. Check the setting again.

Matomo version

5.2.0

PHP version

8.3

Server operating system

Linux

What browsers are you seeing the problem on?

No response

Computer operating system

Ubuntu 22.04

Relevant log output

No response

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• The provided steps to reproduce is a minimal reproducible of the Bug.