Error message 'Passing null to parameter #3' in Joomla Template

When I install the Joomla Cashemir Quickstart files on my server, everything worked, but at the end, after finishing the installation without problems, the following error occurs five times, when opening the website:

Deprecated: header(): Passing null to parameter #3 ($response_code) of type int is deprecated in /var/www/vhosts/xyzxyzxyz.de/libraries/src/Application/WebApplication.php on line 1101

Where is the mistake?

Thanks and kind regards,

Martin

Hi,

Contact with your purchase item author hope they will helped!

Thanks!