Allow 'parentId' is null or negative integer

Author: cklei-carly

src/Support/Utils.php

@@ -49,17 +49,22 @@ public static function buildNestedArray(
     {
         $branch = [];
         $parentId = is_numeric($parentId) ? intval($parentId) : $parentId;
-        if (blank($parentId)) {
-            $parentId = self::defaultParentId();
-        }
+        // if (blank($parentId)) {
+        //     $parentId = self::defaultParentId();
+        // }
         $primaryKeyName = $primaryKeyName ?: 'id';
         $parentKeyName = $parentKeyName ?: static::parentColumnName();
         $childrenKeyName = $childrenKeyName ?: static::defaultChildrenKeyName();
 
         $nodeGroups = collect($nodes)->groupBy(fn ($node) => $node[$parentKeyName])->sortKeys();
         foreach ($nodeGroups as $pk => $nodeGroup) {
             $pk = is_numeric($pk) ? intval($pk) : $pk;
-            if ($pk === $parentId) {
+            if ( 
+                ($pk === $parentId) 
+                // Allow parentId is nullable or negative number
+                // https://github.com/solutionforest/filament-tree/issues/28
+                || (($pk === '' || $pk <= 0) && $parentId <= 0) 
+            ) {
                 foreach ($nodeGroup as $node) {
                     $node = collect($node)->toArray();