feat: groups price calculator admin crud, booking/offer flow and api

src/Twig/AppRuntime.php

@@ -209,6 +209,11 @@ class AppRuntime implements RuntimeExtensionInterface
         $labels = [];
 
         foreach ($form->children as $child) {
+            // Buttons (e.g. submit buttons) aren't validatable fields and have no errors/valid vars.
+            if (!\array_key_exists('errors', $child->vars)) {
+                continue;
+            }
+
             $hasErrors = \count($child->vars['errors']) > 0;
             $hasInvalidChildren = false === $child->vars['valid'];