The website encountered an unexpected error after installation.

Problem/Motivation

I am getting "The website encountered an unexpected error" on page after theme installation. i am using drupal 10 and installed theme using composer.

The website encountered an unexpected error. Try again later.

Error: Call to a member function getPlugin() on null in sailor_theme_suggestions_block_alter() (line 274 of themes\contrib\sailor\sailor.theme).
Drupal\Core\Theme\ThemeManager->alterForTheme(Object, 'theme_suggestions', Array, Array, 'block') (Line: 467)
Drupal\Core\Theme\ThemeManager->alter(Array, Array, Array, 'block') (Line: 394)
Drupal\Core\Theme\ThemeManager->buildThemeHookSuggestions('block', '', Array) (Line: 220)
Drupal\Core\Theme\ThemeManager->render('block', Array) (Line: 480)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 493)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
Drupal\Core\Render\Renderer->render(Array) (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 52)
__TwigTemplate_e786ab81200095ac28d8c67c536ed9fa->doDisplay(Array, Array) (Line: 394)
Twig\Template->displayWithErrorHandling(Array, Array) (Line: 367)
Twig\Template->display(Array) (Line: 379)
Twig\Template->render(Array) (Line: 38)
Twig\TemplateWrapper->render(Array) (Line: 39)
twig_render_template('core/themes/stable9/layouts/layout_discovery/onecol/layout--onecol.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('layout__onecol', Array) (Line: 480)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 493)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 493)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
Drupal\Core\Render\Renderer->render(Array) (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 46)
__TwigTemplate_f530468bce900fa0c89761cb82855847->doDisplay(Array, Array) (Line: 394)
Twig\Template->displayWithErrorHandling(Array, Array) (Line: 367)
Twig\Template->display(Array) (Line: 379)
Twig\Template->render(Array) (Line: 38)
Twig\TemplateWrapper->render(Array) (Line: 39)
twig_render_template('core/themes/stable9/templates/user/user.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('user', Array) (Line: 480)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
Drupal\Core\Render\Renderer->render(Array) (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 75)
__TwigTemplate_2f16da80209b967c03fae68155621bcb->doDisplay(Array, Array) (Line: 394)
Twig\Template->displayWithErrorHandling(Array, Array) (Line: 367)
Twig\Template->display(Array) (Line: 379)
Twig\Template->render(Array) (Line: 38)
Twig\TemplateWrapper->render(Array) (Line: 39)
twig_render_template('core/themes/stable9/templates/content/node.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('node', Array) (Line: 480)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
Drupal\Core\Render\Renderer->render(Array) (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 60)
__TwigTemplate_afe2bdb3ceeca27d33eea837cfdd05ba->doDisplay(Array, Array) (Line: 394)
Twig\Template->displayWithErrorHandling(Array, Array) (Line: 367)
Twig\Template->display(Array) (Line: 379)
Twig\Template->render(Array) (Line: 38)
Twig\TemplateWrapper->render(Array) (Line: 39)
twig_render_template('core/themes/stable9/templates/views/views-view-unformatted.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('views_view_unformatted', Array) (Line: 480)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 493)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
Drupal\Core\Render\Renderer->render(Array) (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 85)
__TwigTemplate_e91b99ff7b1d7e16016bea42d858757a->doDisplay(Array, Array) (Line: 394)
Twig\Template->displayWithErrorHandling(Array, Array) (Line: 367)
Twig\Template->display(Array) (Line: 379)
Twig\Template->render(Array) (Line: 38)
Twig\TemplateWrapper->render(Array) (Line: 39)
twig_render_template('core/themes/stable9/templates/views/views-view.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('views_view', Array) (Line: 480)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 493)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 240)
Drupal\Core\Render\Renderer->render(Array, ) (Line: 238)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 627)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 231)
Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 128)
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: 58)
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: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->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: 704)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes