30. Substring with Concatenation of All Words

114. Flatten Binary Tree to Linked List/Program.cs

@@ -22,7 +22,7 @@ static TreeNode? BuildTreeFromLevelOrder(int?[] data)
 	if (data.Length == 0 || data[0] == null)
 		return null;
 
-	var root = new TreeNode(data[0].Value);
+	var root = new TreeNode(data[0]!.Value);
 	var queue = new Queue<TreeNode>();
 	queue.Enqueue(root);