Undefined index: translatable in Drupal\docson\Form\EntityBundlePicker->buildForm()

On the "Schema Selector" page (/docson), selecting an "Entity Type" throws the following notice:
Notice: Undefined index: translatable in Drupal\docson\Form\EntityBundlePicker->buildForm() (line 118 of /home/vagrant/docroot/drupal8_site/web/modules/contrib/docson/src/Form/EntityBundlePicker.php) #0 /home/vagrant/docroot/drupal8_site/web/core/includes/bootstrap.inc(552): _drupal_error_handler_real(8, 'Undefined index...', '/home/vagrant/d...', 118, Array) #1 /home/vagrant/docroot/drupal8_site/web/modules/contrib/docson/src/Form/EntityBundlePicker.php(118): _drupal_error_handler(8, 'Undefined index...', '/home/vagrant/d...', 118, Array) #2 [internal function]: Drupal\docson\Form\EntityBundlePicker->buildForm(Array, Object(Drupal\Core\Form\FormState)) #3 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/Form/FormBuilder.php(514): call_user_func_array(Array, Array) #4 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/Form/FormBuilder.php(364): Drupal\Core\Form\FormBuilder->retrieveForm('docson_entity_b...', Object(Drupal\Core\Form\FormState)) #5 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/Form/FormBuilder.php(621): Drupal\Core\Form\FormBuilder->rebuildForm('docson_entity_b...', Object(Drupal\Core\Form\FormState), Array) #6 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/Form/FormBuilder.php(314): Drupal\Core\Form\FormBuilder->processForm('docson_entity_b...', Array, Object(Drupal\Core\Form\FormState)) #7 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/Controller/FormController.php(74): Drupal\Core\Form\FormBuilder->buildForm('docson_entity_b...', Object(Drupal\Core\Form\FormState)) #8 [internal function]: Drupal\Core\Controller\FormController->getContentResult(Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\Core\Routing\RouteMatch)) #9 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array) #10 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/Render/Renderer.php(574): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #11 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #12 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) #13 [internal function]: Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #14 /home/vagrant/docroot/drupal8_site/vendor/symfony/http-kernel/HttpKernel.php(144): call_user_func_array(Object(Closure), Array) #15 /home/vagrant/docroot/drupal8_site/vendor/symfony/http-kernel/HttpKernel.php(64): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #16 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #17 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #18 /home/vagrant/docroot/drupal8_site/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(99): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #19 /home/vagrant/docroot/drupal8_site/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(78): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #20 /home/vagrant/docroot/drupal8_site/web/core/modules/ban/src/BanMiddleware.php(50): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #21 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\ban\BanMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #22 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(50): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #23 /home/vagrant/docroot/drupal8_site/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #24 /home/vagrant/docroot/drupal8_site/web/core/lib/Drupal/Core/DrupalKernel.php(656): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #25 /home/vagrant/docroot/drupal8_site/web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #26 {main}.