Error in comments section

Hello,

After activating the plugin, I went to plugin settings. Updated the settings and then submitted a test comment. The plugin displayed the first letter of comment author name. But I also got this warning on the comments area:

Warning: Missing argument 5 for WP_First_Letter_Avatar::set_avatar() in /home/username/sitename/wp-content/plugins/wp-first-letter-avatar/wp-first-letter-avatar.php on line 92

https://ww.wp.xz.cn/plugins/wp-first-letter-avatar/