line 430 of preprocess.in

I am using Drupal 8.8.3 with theme Pixture Reloaded 8.x-3.0, built on Adaptive Theme 8.x-3.1. After installing some modules and developing the site, I got this error message.

Notice: Undefined index: display_submitted in at_core_preprocess_node() (line 430 of themes/adaptivetheme/at_core/includes/preprocess.inc).
Notice: Undefined index: display_submitted in at_core_preprocess_node() (line 430 of themes/adaptivetheme/at_core/includes/preprocess.inc).
Notice: Undefined index: display_submitted in at_core_preprocess_node() (line 430 of themes/adaptivetheme/at_core/includes/preprocess.inc).
Notice: Undefined index: display_submitted in at_core_preprocess_node() (line 430 of themes/adaptivetheme/at_core/includes/preprocess.inc).

I come to the file, and just right before line 430, it says:
// SEE https://drupal.org/node/2004252 or a follow up issue.
if ($variables['display_submitted']) {

I follow the link but the patch does not match the current version. I also look at
https://api.drupal.org/api/drupal/core%21modules%21node%21node.module/fu...

But it does not work for me either. I look around without any success. It seems that the problem has already been identified, and I am looking for a solution.

I am not sure the problem is from Drupal Core, AT, or Pixture Reloaded. Thank you for your help.

I am new to Drupal.