Not working with webform?

Hi,
in a Thunder distribution environment I tried to use menu Link Modal for working with webform (Version: 8.x-5.0-rc24). Without success.

Notice: Undefined index: class in menu_link_modal_set_attributes() (Zeile 104 in .../modules/menu_link_modal/menu_link_modal.module) #0 .../core/includes/bootstrap.inc(584): _drupal_error_handler_real(8, 'Undefined index...', '/home/www/doc/2...', 104, Array) #1 .../modules/menu_link_modal/menu_link_modal.module(104): _drupal_error_handler(8, 'Undefined index...', '/home/www/doc/2...', 104, Array) #2 .../modules/menu_link_modal/menu_link_modal.module(82): menu_link_modal_set_attributes(Array, true) #3 .../core/lib/Drupal/Core/Theme/ThemeManager.php(287): menu_link_modal_preprocess_menu(Array, 'menu', Array) #4 .../core/lib/Drupal/Core/Render/Renderer.php(437): Drupal\Core\Theme\ThemeManager->render('menu', Array) #5 .../core/lib/Drupal/Core/Render/Renderer.php(195): Drupal\Core\Render\Renderer->doRender(Array, false) #6 .../core/lib/Drupal/Core/Template/TwigExtension.php(490): Drupal\Core\Render\Renderer->render(Array) #7 .../sites/default/files/php/twig/5bdc4626b2cc3_block--system-menu-block._5tGDWu_59l8fD_aqNzgajmaw5/kr9BP3u97wkMWCQIgCqVrfuerkijqMBaAhozj9QZWxQ.php(86): Drupal\Core\Template\TwigExtension->escapeFilter(Object(Drupal\Core\Template\TwigEnvironment), Array, 'html', NULL, true) #8 .../vendor/twig/twig/lib/Twig/Template.php(215): __TwigTemplate_b885b95abfc334b7e0f01023680f606611af99fbc41badd6deb4fe697a747f94->block_content(Array, Array) #9 .../sites/default/files/php/twig/5bdc4626b2cc3_block--system-menu-block._2hNSCNK6Y2jmAWQaMH3vksp4p/bDBLxL7jLNjIQmvMxmUNhldCHmibZm0tAH5SGBc4Wmk.php(82): Twig_Template->displayBlock('content', Array, Array) #10 .../vendor/twig/twig/lib/Twig/Template.php(432): __TwigTemplate_bcf730392e18d13056f9a940f0627ea8e84e3406b2877b6391fdc398a09c6201->doDisplay(Array, Array) #11 .../vendor/twig/twig/lib/Twig/Template.php(403): Twig_Template->displayWithErrorHandling(Array, Array) #12 .../sites/default/files/php/twig/5bdc4626b2cc3_block--system-menu-block._5tGDWu_59l8fD_aqNzgajmaw5/kr9BP3u97wkMWCQIgCqVrfuerkijqMBaAhozj9QZWxQ.php(53): Twig_Template->display(Array, Array) #13 .../vendor/twig/twig/lib/Twig/Template.php(432): __TwigTemplate_b885b95abfc334b7e0f01023680f606611af99fbc41badd6deb4fe697a747f94->doDisplay(Array, Array) #14 .../vendor/twig/twig/lib/Twig/Template.php(403): Twig_Template->displayWithErrorHandling(Array, Array) #15 .../vendor/twig/twig/lib/Twig/Template.php(411): Twig_Template->display(Array) #16 .../core/themes/engines/twig/twig.engine(64): Twig_Template->render(Array) #17 .../core/lib/Drupal/Core/Theme/ThemeManager.php(384): twig_render_template('themes/custom/n...', Array) #18 .../core/lib/Drupal/Core/Render/Renderer.php(437): Drupal\Core\Theme\ThemeManager->render('block', Array) #19 .../core/lib/Drupal/Core/Render/Renderer.php(450): Drupal\Core\Render\Renderer->doRender(Array) #20 .../core/lib/Drupal/Core/Render/Renderer.php(195): Drupal\Core\Render\Renderer->doRender(Array, false) #21 .../core/lib/Drupal/Core/Template/TwigExtension.php(490): Drupal\Core\Render\Renderer->render(Array) #22 .../sites/default/files/php/twig/5bdc4626b2cc3_page.html.twig_pI295AV2uPAH0XaveJ17e27aa/A0seuRGAiKHIb9CfxBBismlHCsPuAamKK63nz0Ysv0M.php(74): Drupal\Core\Template\TwigExtension->escapeFilter(Object(Drupal\Core\Template\TwigEnvironment), Array, 'html', NULL, true) #23 .../vendor/twig/twig/lib/Twig/Template.php(432): __TwigTemplate_bfc033a8989f6bff7bb79e11865577f2c20ac710acb7f08804f702b374817b0e->doDisplay(Array, Array) #24 .../vendor/twig/twig/lib/Twig/Template.php(403): Twig_Template->displayWithErrorHandling(Array, Array) #25 .../vendor/twig/twig/lib/Twig/Template.php(411): Twig_Template->display(Array) #26 .../core/themes/engines/twig/twig.engine(64): Twig_Template->render(Array) #27 .../core/lib/Drupal/Core/Theme/ThemeManager.php(384): twig_render_template('themes/custom/n...', Array) #28 .../core/lib/Drupal/Core/Render/Renderer.php(437): Drupal\Core\Theme\ThemeManager->render('page', Array) #29 .../core/lib/Drupal/Core/Render/Renderer.php(195): Drupal\Core\Render\Renderer->doRender(Array, false) #30 .../core/lib/Drupal/Core/Template/TwigExtension.php(490): Drupal\Core\Render\Renderer->render(Array) #31 .../sites/default/files/php/twig/5bdc4626b2cc3_html.html.twig_gQv-GORxUVif_Pag4s-5z2NkO/3dipVOW8lEc9eNaOj9CIocBmPeI8LqLiIqrJs6tUhKs.php(90): Drupal\Core\Template\TwigExtension->escapeFilter(Object(Drupal\Core\Template\TwigEnvironment), Array, 'html', NULL, true) #32 .../vendor/twig/twig/lib/Twig/Template.php(432): __TwigTemplate_be8c7bbb9c824f2826368d7c8da984c6279779db72a67fd8056a00bb23b816f2->doDisplay(Array, Array) #33 .../vendor/twig/twig/lib/Twig/Template.php(403): Twig_Template->displayWithErrorHandling(Array, Array) #34 .../vendor/twig/twig/lib/Twig/Template.php(411): Twig_Template->display(Array) #35 .../core/themes/engines/twig/twig.engine(64): Twig_Template->render(Array) #36 .../core/lib/Drupal/Core/Theme/ThemeManager.php(384): twig_render_template('core/themes/cla...', Array) #37 .../core/lib/Drupal/Core/Render/Renderer.php(437): Drupal\Core\Theme\ThemeManager->render('html', Array) #38 .../core/lib/Drupal/Core/Render/Renderer.php(195): Drupal\Core\Render\Renderer->doRender(Array, false) #39 .../core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(147): Drupal\Core\Render\Renderer->render(Array) #40 .../core/lib/Drupal/Core/Render/Renderer.php(582): Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() #41 .../core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(148): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #42 .../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)) #43 [internal function]: Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object(Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent), 'kernel.view', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher)) #44 .../core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(111): call_user_func(Array, Object(Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent), 'kernel.view', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher)) #45 .../vendor/symfony/http-kernel/HttpKernel.php(156): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.view', Object(Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent)) #46 .../vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #47 .../core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #48 .../core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #49 .../core/modules/page_cache/src/StackMiddleware/PageCache.php(99): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #50 .../core/modules/page_cache/src/StackMiddleware/PageCache.php(78): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #51 .../core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #52 .../core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #53 .../vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #54 .../core/lib/Drupal/Core/DrupalKernel.php(665): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #55 .../index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #56 {main}.