Error message
Warning: foreach() argument must be of type array|object, null given in Drupal\pollions_custom\Form\PrevnextForm->buildForm() (line 59 of modules/custom/pollions_custom/src/Form/PrevnextForm.php).
Drupal\pollions_custom\Form\PrevnextForm->buildForm(Array, Object)
call_user_func_array(Array, Array) (Line: 536)
Drupal\Core\Form\FormBuilder->retrieveForm('prev_next_form', Object) (Line: 284)
Drupal\Core\Form\FormBuilder->buildForm('Drupal\pollions_custom\Form\PrevnextForm', Object) (Line: 224)
Drupal\Core\Form\FormBuilder->getForm('Drupal\pollions_custom\Form\PrevnextForm') (Line: 21)
Drupal\pollions_custom\Plugin\Block\PrevnextBlock->build() (Line: 171)
Drupal\block\BlockViewBuilder::preRender(Array)
call_user_func_array('Drupal\block\BlockViewBuilder::preRender', Array) (Line: 113)
Drupal\Core\Render\Renderer->doTrustedCallback('Drupal\block\BlockViewBuilder::preRender', Array, 'Render #pre_render callbacks must be methods of a class that implements \Drupal\Core\Security\TrustedCallbackInterface or be an anonymous function. The callback was %s. See https://www.drupal.org/node/2966725', 'exception', 'Drupal\Core\Render\Element\RenderCallbackInterface') (Line: 870)
Drupal\Core\Render\Renderer->doCallback('#pre_render', 'Drupal\block\BlockViewBuilder::preRender', Array) (Line: 432)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 504)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 248)
Drupal\Core\Render\Renderer->render(Array) (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 191)
__TwigTemplate_b131b2fc6584c37017e9401591d3f4af->doDisplay(Array, Array) (Line: 360)
Twig\Template->yield(Array) (Line: 335)
Twig\Template->render(Array) (Line: 38)
Twig\TemplateWrapper->render(Array) (Line: 33)
twig_render_template('themes/custom/pollions/templates/layout/page--poll--%.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('page', Array) (Line: 491)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 248)
Drupal\Core\Render\Renderer->render(Array) (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 109)
__TwigTemplate_1eb2c6fb2486ac6490bc3a21319b8fb5->doDisplay(Array, Array) (Line: 360)
Twig\Template->yield(Array) (Line: 335)
Twig\Template->render(Array) (Line: 38)
Twig\TemplateWrapper->render(Array) (Line: 33)
twig_render_template('themes/custom/pollions/templates/layout/html.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('html', Array) (Line: 491)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 248)
Drupal\Core\Render\Renderer->render(Array) (Line: 158)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 638)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 153)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object)
call_user_func(Array, Object, 'kernel.view', Object) (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.view') (Line: 186)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 53)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle(Object, 1, 1) (Line: 32)
Drupal\big_pipe\StackMiddleware\ContentLength->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 36)
Drupal\Core\StackMiddleware\AjaxPageState->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object, 1, 1) (Line: 741)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)
Design check