Fix PHP 8.5 deprecations: (#10)

Deprecated: Using null as an array offset is deprecated, use an empty string instead

Author: xificurk

src/ComponentModel/Container.php

@@ -65,7 +65,7 @@ public function addComponent(IComponent $component, ?string $name, ?string $inse
 		// user checking
 		$this->validateChildComponent($component);
 
-		if (isset($this->components[$insertBefore])) {
+		if ($insertBefore !== null && isset($this->components[$insertBefore])) {
 			$tmp = [];
 			foreach ($this->components as $k => $v) {
 				if ((string) $k === $insertBefore) {