Undefined array key ""

Problem/Motivation

I'm intermittently running into this warning on our charts pages. It'll go away for a while and then show back up. I'm not sure where to look to address this issue. I've also tried saving all the views again to see if they stored old settings, but it still happens. We're using Views Highcharts.

Also, I've tried using a grouping field, but it seems to force the wrong behavior in our chart data. Not grouping causes the correct chart behavior, so we're not grouping at the moment if that's the issue. I saw some other issue that indicated that the data needed to have a grouping field, but that makes more problems than it solves.

Warning: Undefined array key "" in Drupal\charts\Plugin\views\style\ChartsPluginStyleChart->renderGrouping() (line 581 of modules/contrib/charts/src/Plugin/views/style/ChartsPluginStyleChart.php).
Drupal\charts\Plugin\views\style\ChartsPluginStyleChart->renderGrouping(Array, Array, 1) (Line: 410)
Drupal\charts\Plugin\views\style\ChartsPluginStyleChart->render() (Line: 2177)
Drupal\views\Plugin\views\display\DisplayPluginBase->render() (Line: 1592)
Drupal\views\ViewExecutable->render() (Line: 133)
Drupal\views\Plugin\views\display\Block->execute() (Line: 1689)
Drupal\views\ViewExecutable->executeDisplay('block_6', Array) (Line: 81)
Drupal\views\Element\View::preRenderViewElement(Array) (Line: 61)
Drupal\views\Plugin\Block\ViewsBlock->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: 83)
__TwigTemplate_736371f95f320c129ad73ad480eccf1d->block_content(Array, Array) (Line: 430)
Twig\Template->yieldBlock('content', Array, Array) (Line: 69)
__TwigTemplate_736371f95f320c129ad73ad480eccf1d->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/MY_THEME/templates/block/block.html.twig', Array) (Line: 348)
Drupal\Core\Theme\ThemeManager->render('block', Array) (Line: 491)
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: 297)
__TwigTemplate_fe2d463454c5186a477d8095af318e93->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/MY_THEME/templates/layout/page.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: 84)
__TwigTemplate_e37fe822a22a1dd04a6b4fc3a715dc00->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/MY_THEME/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: 159)
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: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 57)
Drupal\advban\AdvbanMiddleware->handle(Object, 1, 1) (Line: 50)
Drupal\ban\BanMiddleware->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)

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes