Hello,
when i try to rearrange fields in view that has rss Feedenabled i get:
Error: Call to a member function get() on null w Drupal\views_ui\Form\Ajax\Rearrange->submitForm() (linia 156 w /var/www/html/drupal8/core/modules/views_ui/src/Form/Ajax/Rearrange.php) #0 [internal function]: Drupal\views_ui\Form\Ajax\Rearrange->submitForm(Array, Object(Drupal\Core\Form\FormState)) #1 /var/www/html/drupal8/core/modules/views_ui/src/ViewUI.php(258): call_user_func_array(Array, Array) #2 [internal function]: Drupal\views_ui\ViewUI->standardSubmit(Array, Object(Drupal\Core\Form\FormState)) #3 /var/www/html/drupal8/core/lib/Drupal/Core/Form/FormSubmitter.php(111): call_user_func_array(Array, Array) #4 /var/www/html/drupal8/core/lib/Drupal/Core/Form/FormSubmitter.php(51): Drupal\Core\Form\FormSubmitter->executeSubmitHandlers(Array, Object(Drupal\Core\Form\FormState)) #5 /var/www/html/drupal8/core/lib/Drupal/Core/Form/FormBuilder.php(590): Drupal\Core\Form\FormSubmitter->doSubmitForm(Array, Object(Drupal\Core\Form\FormState)) #6 /var/www/html/drupal8/core/lib/Drupal/Core/Form/FormBuilder.php(319): Drupal\Core\Form\FormBuilder->processForm('views_ui_rearra...', Array, Object(Drupal\Core\Form\FormState)) #7 /var/www/html/drupal8/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php(214): Drupal\Core\Form\FormBuilder->buildForm('views_ui_rearra...', Object(Drupal\Core\Form\FormState)) #8 /var/www/html/drupal8/core/lib/Drupal/Core/Render/Renderer.php(582): Drupal\views_ui\Form\Ajax\ViewsFormBase->Drupal\views_ui\Form\Ajax\{closure}() #9 /var/www/html/drupal8/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php(216): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #10 /var/www/html/drupal8/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php(125): Drupal\views_ui\Form\Ajax\ViewsFormBase->ajaxFormWrapper('Drupal\\views_ui...', Object(Drupal\Core\Form\FormState)) #11 /var/www/html/drupal8/core/modules/views_ui/src/Form/Ajax/Rearrange.php(37): Drupal\views_ui\Form\Ajax\ViewsFormBase->getForm(Object(Drupal\views_ui\ViewUI), 'page_1', 'ajax') #12 [internal function]: Drupal\views_ui\Form\Ajax\Rearrange->getForm(Object(Drupal\views_ui\ViewUI), 'page_1', 'ajax', 'field') #13 /var/www/html/drupal8/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array) #14 /var/www/html/drupal8/core/lib/Drupal/Core/Render/Renderer.php(582): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #15 /var/www/html/drupal8/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #16 /var/www/html/drupal8/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) #17 /var/www/html/drupal8/vendor/symfony/http-kernel/HttpKernel.php(151): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #18 /var/www/html/drupal8/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #19 /var/www/html/drupal8/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #20 /var/www/html/drupal8/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #21 /var/www/html/drupal8/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #22 /var/www/html/drupal8/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #23 /var/www/html/drupal8/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #24 /var/www/html/drupal8/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #25 /var/www/html/drupal8/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #26 /var/www/html/drupal8/core/lib/Drupal/Core/DrupalKernel.php(693): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #27 /var/www/html/drupal8/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #28 {main}.
This error doesn't appear if i disable or delete Feed.