diff --git a/core/src/raw/adapters/kv/api.rs b/core/src/raw/adapters/kv/api.rs
index 3ee1b57639b..8f9b8e96583 100644
--- a/core/src/raw/adapters/kv/api.rs
+++ b/core/src/raw/adapters/kv/api.rs
@@ -26,30 +26,37 @@ use crate::Capability;
 use crate::Scheme;
 use crate::*;
 
-/// ScanIter is the async iterator returned by `Adapter::scan`.
+/// Scan is the async iterator returned by `Adapter::scan`.
 pub trait Scan: Send + Sync + Unpin {
     /// Fetch the next key in the current key prefix
     ///
-    /// `None` means no further key will be returned
-    fn next(&mut self) -> impl Future<Output = Option<Result<String>>> + MaybeSend;
+    /// `Ok(None)` means no further key will be returned
+    fn next(&mut self) -> impl Future<Output = Result<Option<String>>> + MaybeSend;
 }
 
 /// A noop implementation of Scan
 impl Scan for () {
-    async fn next(&mut self) -> Option<Result<String>> {
-        None
+    async fn next(&mut self) -> Result<Option<String>> {
+        Ok(None)
     }
 }
 
-/// A ScanIterator implementation for all trivial non-async iterators
+/// A Scan implementation for all trivial non-async iterators
 pub struct ScanStdIter<I>(I);
 
+#[cfg(any(
+    feature = "services-cloudflare-kv",
+    feature = "services-etcd",
+    feature = "services-nebula-graph",
+    feature = "services-rocksdb",
+    feature = "services-sled"
+))]
 impl<I> ScanStdIter<I>
 where
     I: Iterator<Item = Result<String>> + Unpin + Send + Sync,
 {
     /// Create a new ScanStdIter from an Iterator
-    pub fn new(inner: I) -> Self {
+    pub(crate) fn new(inner: I) -> Self {
         Self(inner)
     }
 }
@@ -58,8 +65,8 @@ impl<I> Scan for ScanStdIter<I>
 where
     I: Iterator<Item = Result<String>> + Unpin + Send + Sync,
 {
-    async fn next(&mut self) -> Option<Result<String>> {
-        self.0.next()
+    async fn next(&mut self) -> Result<Option<String>> {
+        self.0.next().transpose()
     }
 }
 
@@ -67,17 +74,17 @@ where
 pub type Scanner = Box<dyn ScanDyn>;
 
 pub trait ScanDyn: Unpin + Send + Sync {
-    fn next_dyn(&mut self) -> BoxedFuture<Option<Result<String>>>;
+    fn next_dyn(&mut self) -> BoxedFuture<Result<Option<String>>>;
 }
 
 impl<T: Scan + ?Sized> ScanDyn for T {
-    fn next_dyn(&mut self) -> BoxedFuture<Option<Result<String>>> {
+    fn next_dyn(&mut self) -> BoxedFuture<Result<Option<String>>> {
         Box::pin(self.next())
     }
 }
 
 impl<T: ScanDyn + ?Sized> Scan for Box<T> {
-    async fn next(&mut self) -> Option<Result<String>> {
+    async fn next(&mut self) -> Result<Option<String>> {
         self.deref_mut().next_dyn().await
     }
 }
diff --git a/core/src/raw/adapters/kv/backend.rs b/core/src/raw/adapters/kv/backend.rs
index 520f14351ed..bdbe8202a7b 100644
--- a/core/src/raw/adapters/kv/backend.rs
+++ b/core/src/raw/adapters/kv/backend.rs
@@ -206,7 +206,7 @@ where
     }
 
     async fn inner_next(&mut self) -> Result<Option<oio::Entry>> {
-        Ok(self.inner.next().await.transpose()?.map(|v| {
+        Ok(self.inner.next().await?.map(|v| {
             let mode = if v.ends_with('/') {
                 EntryMode::DIR
             } else {
diff --git a/core/src/raw/adapters/kv/mod.rs b/core/src/raw/adapters/kv/mod.rs
index ef6d4793fee..c03c8d71b80 100644
--- a/core/src/raw/adapters/kv/mod.rs
+++ b/core/src/raw/adapters/kv/mod.rs
@@ -23,7 +23,14 @@ mod api;
 pub use api::Adapter;
 pub use api::Metadata;
 pub use api::Scan;
-pub use api::ScanStdIter;
+#[cfg(any(
+    feature = "services-cloudflare-kv",
+    feature = "services-etcd",
+    feature = "services-nebula-graph",
+    feature = "services-rocksdb",
+    feature = "services-sled"
+))]
+pub(crate) use api::ScanStdIter;
 pub use api::Scanner;
 
 mod backend;
diff --git a/core/src/services/sqlite/backend.rs b/core/src/services/sqlite/backend.rs
index f0f59da6301..06158048341 100644
--- a/core/src/services/sqlite/backend.rs
+++ b/core/src/services/sqlite/backend.rs
@@ -196,7 +196,7 @@ impl Adapter {
 }
 
 #[self_referencing]
-pub struct SqlStream {
+pub struct SqliteScanner {
     pool: SqlitePool,
     query: String,
 
@@ -205,7 +205,7 @@ pub struct SqlStream {
     stream: BoxStream<'this, Result<String>>,
 }
 
-impl Stream for SqlStream {
+impl Stream for SqliteScanner {
     type Item = Result<String>;
 
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
@@ -213,16 +213,16 @@ impl Stream for SqlStream {
     }
 }
 
-unsafe impl Sync for SqlStream {}
+unsafe impl Sync for SqliteScanner {}
 
-impl kv::Scan for SqlStream {
-    async fn next(&mut self) -> Option<Result<String>> {
-        <Self as StreamExt>::next(self).await
+impl kv::Scan for SqliteScanner {
+    async fn next(&mut self) -> Result<Option<String>> {
+        <Self as StreamExt>::next(self).await.transpose()
     }
 }
 
 impl kv::Adapter for Adapter {
-    type Scanner = SqlStream;
+    type Scanner = SqliteScanner;
 
     fn metadata(&self) -> kv::Metadata {
         kv::Metadata::new(
@@ -286,7 +286,7 @@ impl kv::Adapter for Adapter {
 
     async fn scan(&self, path: &str) -> Result<Self::Scanner> {
         let pool = self.get_client().await?;
-        let stream = SqlStreamBuilder {
+        let stream = SqliteScannerBuilder {
             pool: pool.clone(),
             query: format!(
                 "SELECT `{}` FROM `{}` WHERE `{}` LIKE $1",