This PHP Notice occurred while attempt to upgrade Zen Cart.

Code:
[29-Jan-2019 20:06:01 UTC] PHP Notice:  Undefined variable: errorHeadingFlag in C:\wamp64\www\zc156\zc_install\includes\template\templates\index_default.php on line 86
[29-Jan-2019 20:06:01 UTC] PHP Stack trace:
[29-Jan-2019 20:06:01 UTC] PHP   1. {main}() C:\wamp64\www\zc156\zc_install\index.php:0
[29-Jan-2019 20:06:01 UTC] PHP   2. require() C:\wamp64\www\zc156\zc_install\index.php:42
[29-Jan-2019 20:06:01 UTC] PHP   3. require() C:\wamp64\www\zc156\zc_install\includes\template\common\tpl_main_page.php:47
So, I decided to inspect all those files listed... and here are codes that it reported as error.

\zc_install\includes\template\templates\index_default.php (line 86)
Code:
<div id="warnErrors" class="errorList">
    <?php if ($errorHeadingFlag) { ?>
        <?php if ($adjustWarnIssues) { ?>
\zc_install\index.php (line 42)
Code:
  if ($controller == 'cli') {
    require DIR_FS_INSTALL . 'includes/cli_controller.php';
  } else {
    require DIR_FS_INSTALL . $page_directory . '/header_php.php';
    require DIR_FS_INSTALL . DIR_WS_INSTALL_TEMPLATE . 'common/html_header.php';
    require DIR_FS_INSTALL . DIR_WS_INSTALL_TEMPLATE . 'common/main_template_vars.php';
    require DIR_FS_INSTALL . DIR_WS_INSTALL_TEMPLATE . 'common/tpl_main_page.php';
  }
\zc_install\includes\template\common\tpl_main_page.php (line 47)
Code:
        <?php } ?>
        <?php require($body_code); ?>
        </div>
While it does not interfere the install process. However, I wanted to report to ensure that this may not lead to future bugs in installation.

-PanZC2020