Erro: Undefined key ID

Hi, my php error log is full of this error, it happens ALL THE TIME, there’s a solution?

023/08/15 11:05:34 [error] 4190390#4190390: *77183 FastCGI sent in stderr: “PHP message: PHP Warning: Undefined array key “id” in /var/www/wordpress/wp-content/plugins/critical-css-for-wp/includes/class-critical-css.php on line 688;

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