Errors after importing live demo of a theme

Hi guys, I’ve downloaded and installed this WordPress Theme https://teslathemes.com/wp-themes/tesla/ and after importing the demo content I get this error

Declaration of Tesla_List_Pages_Walker::start_el() should be compatible with Walker::start_el(&$output, $object, $depth = 0, $args = Array, $current_object_id = 0) in /public/wordpress/test/wp-content/themes/teslawp/functions.php on line 0

Can you please help me out, as this is a free theme and the provider doesn’t offer support for it. Thanks in advance.