Bug: Header element shows error on author archive page, if author has zero posts

Hi support,

I'm pretty sure I have the same problem like those 2 threads:
https://generatepress.com/forums/topic/notice-undefined-offset-0-in-wp-includes-class-wp-query-php-on-line-3275/
https://generatepress.com/forums/topic/php-error-with-gp-pro-plugin-on-custom-author-php-page/

But I think I found the exact cause of this: As soon as you enter anything in the "Content" area (template tags like {{post_title}} or even just simple text) in the Header element for the author archive and the author has zero published posts, then this error/warning is shown:
Warning: Undefined array key 0 in /wp-includes/class-wp-query.php on line 3377

It's not a critical problem, as except for this warning message everything works fine. Tip for anybody with the same problem: This means, simply disabling error_reporting "fixes" this problem (which makes sense for live websites anyway) --> in wp-config.php add:

ini_set( 'display_errors', 'Off' );
ini_set( 'error_reporting', E_ALL );
define( 'WP_DEBUG', false );
define( 'WP_DEBUG_DISPLAY', false );

But yeah, maybe this helps finding the cause of this bug :-)

Thanks and best regards,
Michael