diff --git a/src/SelectTree.php b/src/SelectTree.php
index ac4963f..1845b7e 100644
--- a/src/SelectTree.php
+++ b/src/SelectTree.php
@@ -251,7 +251,7 @@ private function buildTreeFromResults($results, $parent = null): Collection
         // If the tree has strict rull parent root nodes, only retrieve children whose parent is the null value
         // Otherwise, promote other orphaned children to root nodes
         $orphanedResults = $this->hasStrictNullParentRootNodes()
-        ? [$parent => $resultCache[$parent]['children']]
+        ? [$parent => $resultCache[$parent]['children'] ?? []]
         : array_map(
             fn ($item) => $item['children'],
             array_filter(