Fix deprecation warning in PHP 8.3 by ensuring string type in explode() (laravel#55939)

PHP 8.3 introduces a deprecation warning when null is passed to the second parameter of explode(). This change ensures type safety by casting potential null values to strings before calling explode().

This fix ensures compatibility with PHP 8.3 and maintains backward compatibility with previous versions.

Author: Khuthaily

src/Illuminate/Support/NamespacedItemResolver.php

@@ -30,7 +30,7 @@ public function parseKey($key)
         // namespace, and is just a regular configuration item. Namespaces are a
         // tool for organizing configuration items for things such as modules.
         if (! str_contains($key, '::')) {
-            $segments = explode('.', $key);
+            $segments = explode('.', (string) $key);
 
             $parsed = $this->parseBasicSegments($segments);
         } else {
@@ -74,12 +74,12 @@ protected function parseBasicSegments(array $segments)
      */
     protected function parseNamespacedSegments($key)
     {
-        [$namespace, $item] = explode('::', $key);
+        [$namespace, $item] = explode('::', (string) $key);
 
         // First we'll just explode the first segment to get the namespace and group
         // since the item should be in the remaining segments. Once we have these
         // two pieces of data we can proceed with parsing out the item's value.
-        $itemSegments = explode('.', $item);
+        $itemSegments = explode('.', (string) $item);
 
         $groupAndItem = array_slice(
             $this->parseBasicSegments($itemSegments), 1