fix(kv_typed): deser empty bytes with get_ref_slice

tools/kv_typed/src/as_bytes.rs

@@ -67,11 +67,11 @@ mod tests {
 
     #[test]
     fn test_btreeset_as_bytes() {
-        BTreeSet::<u64>::new().as_bytes(|bytes| assert_eq!(bytes, &[]));
+        BTreeSet::<u64>::new().as_bytes(|bytes| assert!(bytes.is_empty()));
     }
     #[test]
     fn test_hashset_as_bytes() {
-        HashSet::<u64>::new().as_bytes(|bytes| assert_eq!(bytes, &[]));
+        HashSet::<u64>::new().as_bytes(|bytes| assert!(bytes.is_empty()));
     }
 }
 

tools/kv_typed/src/backend/leveldb.rs

@@ -171,7 +171,9 @@ impl BackendCol for LevelDbCol {
             self.0
                 .get(ReadOptions::new(), k_bytes)?
                 .map(|bytes| {
-                    if let Some(layout_verified) =
+                    if bytes.is_empty() {
+                        f(&[])
+                    } else if let Some(layout_verified) =
                         zerocopy::LayoutVerified::<_, [V::Elem]>::new_slice(
                             &bytes[V::prefix_len()..],
                         )

tools/kv_typed/src/backend/lmdb.rs

@@ -324,7 +324,9 @@ impl BackendCol for LmdbCol {
                 .get::<_, [u8]>(&self.inner.tree, k_bytes)
                 .to_opt()?
                 .map(|bytes| {
-                    if let Some(layout_verified) =
+                    if bytes.is_empty() {
+                        f(&[])
+                    } else if let Some(layout_verified) =
                         zerocopy::LayoutVerified::<_, [V::Elem]>::new_slice(
                             &bytes[V::prefix_len()..],
                         )

tools/kv_typed/src/backend/memory.rs

@@ -138,7 +138,9 @@ impl BackendCol for MemCol {
             self.tree
                 .get(k_bytes)
                 .map(|bytes| {
-                    if let Some(layout_verified) =
+                    if bytes.is_empty() {
+                        f(&[])
+                    } else if let Some(layout_verified) =
                         zerocopy::LayoutVerified::<_, [V::Elem]>::new_slice(
                             &bytes[V::prefix_len()..],
                         )

tools/kv_typed/src/backend/memory_singleton.rs

@@ -121,7 +121,9 @@ impl BackendCol for MemCol {
         self.0
             .as_ref()
             .map(|bytes| {
-                if let Some(layout_verified) =
+                if bytes.is_empty() {
+                    f(&[])
+                } else if let Some(layout_verified) =
                     zerocopy::LayoutVerified::<_, [V::Elem]>::new_slice(&bytes[V::prefix_len()..])
                 {
                     f(&layout_verified)

tools/kv_typed/src/backend/sled.rs

@@ -121,7 +121,9 @@ impl BackendCol for SledCol {
             self.0
                 .get(k_bytes)?
                 .map(|bytes| {
-                    if let Some(layout_verified) =
+                    if bytes.is_empty() {
+                        f(&[])
+                    } else if let Some(layout_verified) =
                         zerocopy::LayoutVerified::<_, [V::Elem]>::new_slice(
                             &bytes[V::prefix_len()..],
                         )