Problem/Motivation
after adding fullmenu on page getting below error
Deprecated function: substr(): Passing null to parameter #1 ($string) of type string is deprecated in fullmenu_preprocess_block() (line 23 of /var/www/html/web/modules/contrib/fullmenu/fullmenu.module)
#0 /var/www/html/web/core/includes/bootstrap.inc(158): _drupal_error_handler_real(8192, 'substr(): Passi...', '/var/www/html/w...', 23)
#1 [internal function]: _drupal_error_handler(8192, 'substr(): Passi...', '/var/www/html/w...', 23)
#2 /var/www/html/web/modules/contrib/fullmenu/fullmenu.module(23): substr(NULL, 18)
#3 [internal function]: fullmenu_preprocess_block(Array, 'block', Array)
#4 /var/www/html/web/core/lib/Drupal/Core/Theme/ThemeManager.php(285): call_user_func_array('fullmenu_prepro...', Array)
#5 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(433): Drupal\Core\Theme\ThemeManager->render('block', Array)
#6 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(446): Drupal\Core\Render\Renderer->doRender(Array)
#7 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(204): Drupal\Core\Render\Renderer->doRender(Array, false)
#8 /var/www/html/web/core/lib/Drupal/Core/Template/TwigExtension.php(477): Drupal\Core\Render\Renderer->render(Array)
#9 /var/www/html/web/sites/default/files/php/twig/64d09c2074ca9_page.html.twig_-YDCav-tCMlhk7_8halB_opv9/7y9Q4QVOq7ybKmkwWirEtPyUFqAYTYuF0rcPAnHdRq4.php(99): Drupal\Core\Template\TwigExtension->escapeFilter(Object(Drupal\Core\Template\TwigEnvironment), Array, 'html', NULL, true)
#10 /var/www/html/vendor/twig/twig/src/Template.php(394): __TwigTemplate_5d59c251cf2f0b62278d8b70b24f3e59->doDisplay(Array, Array)
#11 /var/www/html/vendor/twig/twig/src/Template.php(367): Twig\Template->displayWithErrorHandling(Array, Array)
#12 /var/www/html/vendor/twig/twig/src/Template.php(379): Twig\Template->display(Array)
#13 /var/www/html/vendor/twig/twig/src/TemplateWrapper.php(40): Twig\Template->render(Array, Array)
#14 /var/www/html/web/core/themes/engines/twig/twig.engine(53): Twig\TemplateWrapper->render(Array)
#15 /var/www/html/web/core/lib/Drupal/Core/Theme/ThemeManager.php(372): twig_render_template('core/themes/oli...', Array)
#16 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(433): Drupal\Core\Theme\ThemeManager->render('page', Array)
#17 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(204): Drupal\Core\Render\Renderer->doRender(Array, false)
#18 /var/www/html/web/core/lib/Drupal/Core/Template/TwigExtension.php(477): Drupal\Core\Render\Renderer->render(Array)
#19 /var/www/html/web/sites/default/files/php/twig/64d09c2074ca9_html.html.twig_C2PuxnCCW8P_e13gXJOwT9sVf/xyJ1pEkbpKfiE2SDSH3R70msuBd4nxwtfKIhz90K6Vw.php(93): Drupal\Core\Template\TwigExtension->escapeFilter(Object(Drupal\Core\Template\TwigEnvironment), Array, 'html', NULL, true)
#20 /var/www/html/vendor/twig/twig/src/Template.php(394): __TwigTemplate_b4ef9c213b4ab59878caa983f010387c->doDisplay(Array, Array)
#21 /var/www/html/vendor/twig/twig/src/Template.php(367): Twig\Template->displayWithErrorHandling(Array, Array)
#22 /var/www/html/vendor/twig/twig/src/Template.php(379): Twig\Template->display(Array)
#23 /var/www/html/vendor/twig/twig/src/TemplateWrapper.php(40): Twig\Template->render(Array, Array)
#24 /var/www/html/web/core/themes/engines/twig/twig.engine(53): Twig\TemplateWrapper->render(Array)
#25 /var/www/html/web/core/lib/Drupal/Core/Theme/ThemeManager.php(372): twig_render_template('core/themes/oli...', Array)
#26 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(433): Drupal\Core\Theme\ThemeManager->render('html', Array)
#27 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(204): Drupal\Core\Render\Renderer->doRender(Array, false)
#28 /var/www/html/web/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(158): Drupal\Core\Render\Renderer->render(Array)
#29 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(580): Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}()
#30 /var/www/html/web/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(159): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure))
#31 /var/www/html/web/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php(90): Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\Core\Routing\CurrentRouteMatch))
#32 [internal function]: Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object(Symfony\Component\HttpKernel\Event\ViewEvent), 'kernel.view', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))
#33 /var/www/html/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(111): call_user_func(Array, Object(Symfony\Component\HttpKernel\Event\ViewEvent), 'kernel.view', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))
#34 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(168): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object(Symfony\Component\HttpKernel\Event\ViewEvent), 'kernel.view')
#35 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(74): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#36 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/Session.php(58): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#37 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(48): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#38 /var/www/html/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#39 /var/www/html/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#40 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(48): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#41 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(51): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#42 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/StackedHttpKernel.php(51): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#43 /var/www/html/web/core/lib/Drupal/Core/DrupalKernel.php(686): Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#44 /var/www/html/web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#45 {main}
Steps to reproduce
install module and place the menu block, will get this error on watchdog.
Remaining tasks
User interface changes
API changes
Data model changes