public Container getContainerById(short containerId) {
    return containerIdToContainerMap.get(containerId);
  }
Gets the {@link Container} of this account with the specified container id.
@param containerId The id of the container to get.
@return The {@link Container} of this account with the specified id, or {@code null} if such a
                   container does not exist.
ambry-api/src/main/java/com/github/ambry/account/Account.java