die with error message if template doesn't exist.

src/Service/Template.php

@@ -12,6 +12,9 @@ namespace App\Service;
  * As I'm not allowed to use 3rd party code like Twig or Smarty I ended up
  * using PHP as a templating engine.
  */
+
+use JetBrains\PhpStorm\NoReturn;
+
 class Template
 {
     /*
@@ -25,13 +28,20 @@ class Template
     /*
      * Add variables to template and throw it out
      */
+    #[NoReturn]
     public function render(string $templateName, array $vars = []): void
     {
+        // assign template vars
         foreach ($vars as $name => $value) {
             $$name = $value;
         }
 
+        $templateFile = $this->templateDir . $templateName;
+        if (file_exists(filename: $templateFile)) {
             include $this->templateDir . $templateName;
+        } else {
+            die("Missing template: $templateFile");
+        }
         exit(0);
     }
 }