suggest fix for warning in php

in line 393

if( isset($_POST['make_faq_page']) && !empty($_POST['make_faq_page'])) {
  	$faq = $_POST['make_faq_page'];
  	update_post_meta( $post_id, 'make_faq_page', $faq);
  }

https://ww.wp.xz.cn/plugins/easy-faq-with-expanding-text/