code: @Override
    public void set(final String name, final UserCredentials other) throws IOException {
      throw new RuntimeException("Not implemented! Attempt to set user " + name + " from: " + other);
    }
docs: Copy credentials from another existing user.
  This method can be called only once per instance.
  This default implementation should never be called.
  @param name Name of the new user.
  @param other Credentials of another user.
  @throws RuntimeException always throws.