Undefined array key 1 in menu_block_theme_suggestions_block_alter()

Thanks @alex.bukach I have committed this for the next release.

Automatically closed - issue fixed for 2 weeks with no activity.

You also need this

function menu_block_theme_suggestions_block_alter(array &$suggestions, array $variables) {
-  if ($suggestions[0] == 'block__menu_block') {
+  if (isset($suggestions[0]) && $suggestions[0] == 'block__menu_block') {
    if (isset($suggestions[1]) && $suggestions[1] == 'block__menu_block') {