message: Don't report an error if a hash file is not found
  This is not an error condition - it usually means that we weren't
  participating in the given era before.
diff: @@ -98,11 +98,12 @@ impl<C: Context> ActiveValidator<C> {
  .as_ref()
  .map(Self::read_last_unit)
  .transpose()
  - .map_err(|err| {
  - warn!(
  + .map_err(|err| match err.kind() {
  + io::ErrorKind::NotFound => (),
  + _ => panic!(
  "got an error reading unit hash file {:?}: {:?}",
  unit_hash_file, err
  - )
  + ),
  })
  .ok()
  .flatten();
  