Undefined array key "children" in recursive call of ps_categorytree.tpl on PHP 8

Start in views/templates/hook/ps_categorytree.tpl, comparing the recursive call around line 34 with the guarded outer call around line 46. Render a page with both leaf and nested categories; done means leaf categories render without PHP 8 undefined-array-key warnings.

Bug description

The recursive categories function in views/templates/hook/ps_categorytree.tpl passes $node.children into its recursive call without a guard. When a node has no children (a leaf category), PHP 8 emits Undefined array key "children" on every render. The outer call site in the same template already uses a guard ({if !empty($categories.children)}), so this looks like a consistency oversight: the fix was applied once but not propagated to the recursive call.

Affected code

views/templates/hook/ps_categorytree.tpl, version 3.0.2 (current master).

{function name="categories" nodes=[] depth=0}
  {strip}
    {if $nodes|count}
      <ul>
        {foreach from=$nodes item=node}
          <li>
            <a href="{$node.link}">{$node.name}</a>
            <div>
              {categories nodes=$node.children depth=$depth+1}   {* line 34, no guard on $node.children *}
            </div>
          </li>
        {/foreach}
      </ul>
    {/if}
  {/strip}
{/function}

<div class="category-tree">
  <ul>
    <li><a href="{$categories.link nofilter}">{$categories.name}</a></li>
    {if !empty($categories.children)}                            {* line 46, guarded here *}
      <li>{categories nodes=$categories.children}</li>
    {/if}
  </ul>
</div>

The outer {if !empty(...)} at line 46 protects the top-level call. The recursive call at line 34 does not.

Steps to reproduce

1. PS 9.x with PHP 8.1+ and ps_categorytree enabled in any hook position.

2. Have at least one category tree where some branches have sub-categories and others do not (any non-trivial catalog).

3. Load any page that renders the widget. Each leaf category iteration emits:

   PHP Warning: Undefined array key "children" in var/cache/prod/smarty/compile/<hash>_ps_categorytree.tpl.php on line 39
   

   The line in the compiled PHP corresponds to the Smarty template line 34.

Expected behavior

Leaf categories should render without warnings, same as the outer guarded branch.

Actual behavior

Every leaf iteration produces a PHP warning in the compiled Smarty template. On our production store with a standard catalog this generates ~50 warnings per day from this widget alone.

Proposed fix

Apply the same guard style already used at the outer call site (line 46) to the recursive call at line 34:

{foreach from=$nodes item=node}
  <li>
    <a href="{$node.link}">{$node.name}</a>
    <div>
      {if !empty($node.children)}
        {categories nodes=$node.children depth=$depth+1}
      {/if}
    </div>
  </li>
{/foreach}

Alternatively, using a Smarty default filter:

{categories nodes=$node.children|default:[] depth=$depth+1}

The first option matches the existing style in the same template.

Environment

• PrestaShop: 9.1.0
• PHP: 8.1
• Module ps_categorytree: 3.0.2