piwik.WARNING: /var/www/html/core/Archive/DataCollection.php(381): Notice - Undefined index: 2021-04-26,2021-05-02

This is a regression from #17817

Backtrace

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wik\ArchiveProcessor\Loader","type":"->"},{"file":"/core/ArchiveProcessor/Loader.php","line":105,"function":"changeIdSite","class":"Piwik\Context","type":"::"},{"file":"/plugins/CoreAdminHome/API.php","line":278,"function":"prepareArchive","class":"Piwik\ArchiveProcessor\Loader","type":"->"},{"function":"archiveReports","class":"Piwik\Plugins\CoreAdminHome\API","type":"->"},