public List<Integer> getAllVersions() {
    List<BlobIDAndVersion> blobIDAndVersions = fetchAllBlobIDAndVersions();
    if (blobIDAndVersions == null) {
      return null;
    } else {
      return blobIDAndVersions.stream().map(BlobIDAndVersion::getVersion).collect(Collectors.toList());
    }
  }
Returns all the versions of {@link Account} metadata as a list. It will return null when the versions are empty.
@return All the versions of {@link Account} metadata.
ambry-account/src/main/java/com/github/ambry/account/RouterStore.java