TemporaryExposureKey: safely initialize with null data

    }

    TemporaryExposureKey(byte[] keyData, int rollingStartIntervalNumber, @RiskLevel int transmissionRiskLevel, int rollingPeriod) {

        this.keyData = keyData;

        this.keyData = (keyData == null ? new byte[0] : keyData);

        this.rollingStartIntervalNumber = rollingStartIntervalNumber;

        this.transmissionRiskLevel = transmissionRiskLevel;

        this.rollingPeriod = rollingPeriod;