code: public Credential setExpiresInSeconds(Long expiresIn) {
      return setExpirationTimeMilliseconds(
          expiresIn == null ? null : clock.currentTimeMillis() + expiresIn * 1000);
    }
docs: Sets the lifetime in seconds of the access token (for example 3600 for an hour from now)
  or {@code null} for none.
  
  <p>
  Overriding is only supported for the purpose of calling the super implementation and changing
  the return type, but nothing else.
  </p>
  
  @param expiresIn lifetime in seconds of the access token (for example 3600 for an hour from
  now) or {@code null} for none