downgrade to kirby v3

kirby/src/Cms/NestCollection.php

@@ -20,6 +20,9 @@ class NestCollection extends BaseCollection
 	 * Converts all objects in the collection
 	 * to an array. This can also take a callback
 	 * function to further modify the array result.
+	 *
+	 * @param \Closure|null $map
+	 * @return array
 	 */
 	public function toArray(Closure $map = null): array
 	{