WordPress reports a bug in one module

This is the message I received by email from WordPress:
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Howdy!

Since WordPress 5.2 there is a built-in feature that detects when a plugin or theme causes a fatal error on your site, and notifies you with this automated email.

In this case, WordPress caught an error with one of your plugins, Shopp.
<snip>
When seeking help with this issue, you may be asked for some of the following information:
WordPress version 5.5.3
Current theme: Rover (version 1.0.0)
Current plugin: Shopp (version 1.4)
PHP version 7.4.11

Error Details
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An error of type E_ERROR was caused in line 493 of the file /home/rover407/public_html/wordpress/wp-content/plugins/shopp/core/library/Markdown.php. Error message: Uncaught Error: Call to a member function prepend() on null in /home/rover407/public_html/wordpress/wp-content/plugins/shopp/core/library/Markdown.php:493
Stack trace:
#0 /home/roverpublic_html/wordpress/wp-content/plugins/shopp/core/library/Markdown.php(124): MarkdownBlockquote->filter(Object(MarkdownText))
#1 /home/rover/public_html/wordpress/wp-content/plugins/shopp/core/library/Markdown.php(114): MarkdownText->getHtml()
#2 /home/rover/public_html/wordpress/wp-admin/includes/class-wp-screen.php(910): MarkdownText->__toString()
#3 /home/rover/public_html/wordpress/wp-admin/admin-header.php(270): WP_Screen->render_screen_meta()
#4 /home/rover/public_html/wordpress/wp-admin/admin.php(239): require_once(‘/home/rover/…’)
#5 {main}
thrown
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I haven’t done any markdowns so haven’t seen the error, but felt I should report it.