Exception in PluginRenderer

The Plugin previewRenderer throws an exception in TYPO3 10.4, when the TYPO3 Website uses the Fluid based page module.

Argument 1 passed to SGalinski\DfTabs\Hooks\PageLayoutView\PluginRenderer::adaptPluginHeaderContent() must be of the type string, null given, called in /path/to/website/httpdocs/typo3conf/ext/df_tabs/Classes/Hooks/PageLayoutView/PluginRenderer.php on line 60

Reason for this is, that the $headerContent variable is null, which seems to be intended.