Fluid partial is not rendered if folder with same name exists
If the following file structure is present:
The partial Foo can not be rendered, because the search order for the partial is:
$paths = array( 'Resources/Private/Partials/@partial', 'Resources/Private/Partialsfirstname.lastname@example.org' );
And the function file_exists checks if the partial exists and the folder is the first one checked and returns true, so Fluid generates an empty rendered partial.
In TYPO3 CMS fluid/Classes/View/TemplateView.php:473
This relates to #39868