message: If serialized state is empty, return None.
diff: @@ -350,6 +350,7 @@ impl Storage {
  {
  let txn = self.env.begin_ro_txn()?;
  let bytes = match txn.get(self.state_store_db, &key) {
  + Ok(slice) if slice.is_empty() => None,
  Ok(slice) => Some(slice.to_owned()),
  Err(lmdb::Error::NotFound) => None,
  Err(err) => return Err(err.into()),
  