Post Author tag

Hello, how do I properly change the Post Author tag that shows up when an author leaves a comment on their own listing?

I found this in the comment_functions.php file

// If current post author is also comment author, make it known visually.
                            ($comment->user_id === $post->post_author) ? '<span>' . __('Post author', 'geodirectory') . '</span>' : ''
                        );

I have updated the ‘Post author’ name and it shows up as it should. But when I run my debug, I am getting these notices:

[14-May-2016 08:59:05 UTC] PHP Notice: Trying to get property of non-object in /home/luckywel/public_html/wp-content/themes/kleo-child/functions.php on line 615

[14-May-2016 08:59:05 UTC] PHP Notice: Undefined variable: post in /home/luckywel/public_html/wp-content/themes/kleo-child/functions.php on line 615

[14-May-2016 08:59:05 UTC] PHP Notice: Trying to get property of non-object in /home/luckywel/public_html/wp-content/themes/kleo-child/functions.php on line 615