Notice: Undefined offset: 1 in Drupal\Core\Asset\LibraryDependencyResolver->doGetDependencies() (line 53 of core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php).

This error occurs when defining attached libraries to custom controllers. Make sure that instead of writing

      '#attached' => [
        'library' => ['timeline.global']
      ]

You change the dot to a slash

      '#attached' => [
        'library' => ['timeline/global']
      ]