Undefined index notice and blank search results

Upgrading to 8.x-1.0-beta6 caused the following issue (downgrading to beta5 fixed this issue).

Basically, when I would do a search, it would run the search and come up with results (and seemed to be the correct number of results), but all the results would be empty li tags. There would be no actual content in the search results, just the "1. 2. 3. 4. ...." I tried uninstalling and reinstalling Custom Search, the only thing that fixed the issue was downgrading to beta5.

I also got the following notice in my log (20+ pages of this notice). "event_category" is a taxonomy vocabulary. I have other vocabularies as well which d not seem to cause any issues, however.

Notice: Undefined index: event_category in Drupal\custom_search\Form\CustomSearchBlockForm->buildForm() (line 220 of /path/to/files/public_html/modules/custom_search/src/Form/CustomSearchBlockForm.php) #0 /path/to/files/public_html/core/includes/bootstrap.inc(552): _drupal_error_handler_real(8, 'Undefined index...', '/path/to/files/p...', 220, Array) #1 /path/to/files/public_html/modules/custom_search/src/Form/CustomSearchBlockForm.php(220): _drupal_error_handler(8, 'Undefined index...', '/path/to/files/p...', 220, Array) #2 [internal function]: Drupal\custom_search\Form\CustomSearchBlockForm->buildForm(Array, Object(Drupal\Core\Form\FormState), Array) #3 /path/to/files/public_html/core/lib/Drupal/Core/Form/FormBuilder.php(514): call_user_func_array(Array, Array) #4 /path/to/files/public_html/core/lib/Drupal/Core/Form/FormBuilder.php(271): Drupal\Core\Form\FormBuilder->retrieveForm('custom_search_b...', Object(Drupal\Core\Form\FormState)) #5 /path/to/files/public_html/core/lib/Drupal/Core/Form/FormBuilder.php(212): Drupal\Core\Form\FormBuilder->buildForm('Drupal\\custom_s...', Object(Drupal\Core\Form\FormState)) #6 /path/to/files/public_html/modules/custom_search/src/Plugin/Block/CustomSearchBlock.php(996): Drupal\Core\Form\FormBuilder->getForm('Drupal\\custom_s...', Array) #7 /path/to/files/public_html/core/modules/block/src/BlockViewBuilder.php(203): Drupal\custom_search\Plugin\Block\CustomSearchBlock->build() #8 [internal function]: Drupal\block\BlockViewBuilder::preRender(Array) #9 /path/to/files/public_html/core/lib/Drupal/Core/Render/Renderer.php(376): call_user_func('Drupal\\block\\Bl...', Array) #10 /path/to/files/public_html/core/lib/Drupal/Core/Render/Renderer.php(448): Drupal\Core\Render\Renderer->doRender(Array) #11 /path/to/files/public_html/core/lib/Drupal/Core/Render/Renderer.php(195): Drupal\Core\Render\Renderer->doRender(Array, false) #12 /path/to/files/public_html/core/lib/Drupal/Core/Template/TwigExtension.php(490): Drupal\Core\Render\Renderer->render(Array) #13 /path/to/files/public_html/sites/default/files/php/twig/590cdfab8e552_page.html.twig_Vs7ItMM-0MskSmI1FduVxDjvr/-IfinQZUsGE1YRp8Q52pCpmN2wgykSIe9909kNLvkVM.php(302): Drupal\Core\Template\TwigExtension->escapeFilter(Object(Drupal\Core\Template\TwigEnvironment), Array, 'html', NULL, true) #14 /path/to/files/public_html/vendor/twig/twig/lib/Twig/Template.php(379): __TwigTemplate_d7626bcf2c6032eef0952067329378f33724d327116cb725b55dd5d718d630bb->doDisplay(Array, Array) #15 /path/to/files/public_html/vendor/twig/twig/lib/Twig/Template.php(347): Twig_Template->displayWithErrorHandling(Array, Array) #16 /path/to/files/public_html/vendor/twig/twig/lib/Twig/Template.php(358): Twig_Template->display(Array) #17 /path/to/files/public_html/core/themes/engines/twig/twig.engine(64): Twig_Template->render(Array) #18 /path/to/files/public_html/core/lib/Drupal/Core/Theme/ThemeManager.php(384): twig_render_template('themes/miamicha...', Array) #19 /path/to/files/public_html/core/lib/Drupal/Core/Render/Renderer.php(435): Drupal\Core\Theme\ThemeManager->render('page', Array) #20 /path/to/files/public_html/core/lib/Drupal/Core/Render/Renderer.php(195): Drupal\Core\Render\Renderer->doRender(Array, false) #21 /path/to/files/public_html/core/lib/Drupal/Core/Template/TwigExtension.php(490): Drupal\Core\Render\Renderer->render(Array) #22 /path/to/files/public_html/sites/default/files/php/twig/590cdfab8e552_html.html.twig_kywmIsA3xyQl7OhNikMd9CjDK/yGaFWQsikeWbwgFCzAiyV4uOeyRnUAfVlSti9hyzVHw.php(169): Drupal\Core\Template\TwigExtension->escapeFilter(Object(Drupal\Core\Template\TwigEnvironment), Array, 'html', NULL, true) #23 /path/to/files/public_html/vendor/twig/twig/lib/Twig/Template.php(379): __TwigTemplate_8e91ef8d872d75a4373b7da4154187768538c2527e2fbf3020966a56a1ac9e13->doDisplay(Array, Array) #24 /path/to/files/public_html/vendor/twig/twig/lib/Twig/Template.php(347): Twig_Template->displayWithErrorHandling(Array, Array) #25 /path/to/files/public_html/vendor/twig/twig/lib/Twig/Template.php(358): Twig_Template->display(Array) #26 /path/to/files/public_html/core/themes/engines/twig/twig.engine(64): Twig_Template->render(Array) #27 /path/to/files/public_html/core/lib/Drupal/Core/Theme/ThemeManager.php(384): twig_render_template('themes/miamicha...', Array) #28 /path/to/files/public_html/core/lib/Drupal/Core/Render/Renderer.php(435): Drupal\Core\Theme\ThemeManager->render('html', Array) #29 /path/to/files/public_html/core/lib/Drupal/Core/Render/Renderer.php(195): Drupal\Core\Render\Renderer->doRender(Array, false) #30 /path/to/files/public_html/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(147): Drupal\Core\Render\Renderer->render(Array) #31 /path/to/files/public_html/core/lib/Drupal/Core/Render/Renderer.php(574): Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() #32 /path/to/files/public_html/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(148): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #33 /path/to/files/public_html/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)) #34 /path/to/files/public_html/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(111): Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object(Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent), 'kernel.view', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher)) #35 /path/to/files/public_html/vendor/symfony/http-kernel/HttpKernel.php(149): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.view', Object(Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent)) #36 /path/to/files/public_html/vendor/symfony/http-kernel/HttpKernel.php(64): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #37 /path/to/files/public_html/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #38 /path/to/files/public_html/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #39 /path/to/files/public_html/core/modules/page_cache/src/StackMiddleware/PageCache.php(99): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #40 /path/to/files/public_html/core/modules/page_cache/src/StackMiddleware/PageCache.php(78): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #41 /path/to/files/public_html/core/modules/ban/src/BanMiddleware.php(50): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #42 /path/to/files/public_html/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\ban\BanMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #43 /path/to/files/public_html/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(50): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #44 /path/to/files/public_html/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #45 /path/to/files/public_html/core/lib/Drupal/Core/DrupalKernel.php(656): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #46 /path/to/files/public_html/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #47 {main}.