fix(query-core): preserve null infinite page params

.changeset/null-page-param-refetch.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/query-core': patch
+---
+
+Preserve a stored `null` first page parameter when refetching an infinite query.

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

@@ -474,6 +474,30 @@ describe('InfiniteQueryBehavior', () => {
     unsubscribe()
   })
 
+  it('should preserve a null first page parameter when refetching', async () => {
+    const key = queryKey()
+    const pageParams: Array<unknown> = []
+    const queryFn = ({ pageParam }: { pageParam: unknown }) => {
+      pageParams.push(pageParam)
+      return String(pageParam)
+    }
+
+    await queryClient.infiniteQuery({
+      queryKey: key,
+      queryFn,
+      initialPageParam: null,
+      getNextPageParam: () => undefined,
+    })
+    await queryClient.infiniteQuery({
+      queryKey: key,
+      queryFn,
+      initialPageParam: 'replacement',
+      getNextPageParam: () => undefined,
+    })
+
+    expect(pageParams).toEqual([null, null])
+  })
+
   it('should not fetch next page when getNextPageParam returns null', async () => {
     const key = queryKey()
 

packages/query-core/src/infiniteQueryBehavior.ts

@@ -97,7 +97,9 @@ export function infiniteQueryBehavior<TQueryFnData, TError, TData, TPageParam>(
           do {
             const param =
               currentPage === 0
-                ? (oldPageParams[0] ?? options.initialPageParam)
+                ? oldPageParams[0] === undefined
+                  ? options.initialPageParam
+                  : oldPageParams[0]
                 : getNextPageParam(options, result)
             if (currentPage > 0 && param == null) {
               break