diff --git a/mini-lsm-starter/src/iterators/merge_iterator.rs b/mini-lsm-starter/src/iterators/merge_iterator.rs
index a3e911d..04eca06 100644
--- a/mini-lsm-starter/src/iterators/merge_iterator.rs
+++ b/mini-lsm-starter/src/iterators/merge_iterator.rs
@@ -42,7 +42,7 @@ impl<I: StorageIterator> Ord for HeapWrapper<I> {
 /// iterators, perfer the one with smaller index.
 pub struct MergeIterator<I: StorageIterator> {
     iters: BinaryHeap<HeapWrapper<I>>,
-    current: HeapWrapper<I>,
+    current: Option<HeapWrapper<I>>,
 }
 
 impl<I: StorageIterator> MergeIterator<I> {