fix(streamedQuery): fall back to initialValue when stream yields no values

.changeset/puny-walls-eat.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/query-core': patch
+---
+
+Fix streamedQuery to avoid returning undefined when the stream yields no values

packages/query-core/src/__tests__/streamedQuery.test.tsx

@@ -128,6 +128,37 @@ describe('streamedQuery', () => {
     unsubscribe()
   })
 
+  test('should handle empty streams', async () => {
+
+    const key = queryKey()
+
+    const observer = new QueryObserver(queryClient, {
+      queryKey: key,
+      queryFn: streamedQuery({
+        streamFn: () => { return {async *[Symbol.asyncIterator]() {}}},
+      }),
+    })
+
+    const unsubscribe = observer.subscribe(vi.fn())
+
+    expect(observer.getCurrentResult()).toMatchObject({
+      status: 'pending',
+      fetchStatus: 'fetching',
+      data: undefined,
+    })
+
+    await vi.advanceTimersByTimeAsync(50)
+
+    expect(observer.getCurrentResult()).toMatchObject({
+      status: 'success',
+      fetchStatus: 'idle',
+      data: [],
+    })
+
+    unsubscribe()
+
+  })
+
   test('should replace on refetch', async () => {
     const key = queryKey()
     const observer = new QueryObserver(queryClient, {

packages/query-core/src/streamedQuery.ts

@@ -94,6 +94,6 @@ export function streamedQuery<
       context.client.setQueryData<TData>(context.queryKey, result)
     }
 
-    return context.client.getQueryData(context.queryKey)!
+    return context.client.getQueryData(context.queryKey) ?? initialValue
   }
 }