Non-Manifesto exception

TypeError: count(): Argument #1 ($value) must be of type Countable|array, null given in /xvar/www/html/readabook.online/mods/template_pages/includes/sidebar_subnavigation.inc:93 Stack trace: #0 /xvar/www/html/readabook.online/mods/template_pages/includes/templates/default-with-sidebar-subnavigation.inc(25): include() #1 /xvar/www/html/readabook.online/mods/template_pages/classes/TemplatePage.php(779): include('...') #2 /xvar/www/html/readabook.online/mods/template_pages/controller.inc(33): Manifesto\Base\TemplatePages\TemplatePage->display() #3 /xvar/www/html/readabook.online/site/themes/readabook/page_layouts/template_pages.tmpl.php(207): include('...') #4 /xvar/www/html/readabook.online/mods/template_pages/module_prep.inc(98): require('...') #5 /xvar/www/html/readabook.online/index.php(114): include('...') #6 {main}