✅ Dealing/resolving nullable warnings

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
    if (!PrerequisitesMet())
    {
        _logger.LogError("the options checked an is NULL");
        throw new InvalidOperationException("prerequisites not met.");
    }

    while (!stoppingToken.IsCancellationRequested)
    {
        try
        {
            XDocument doc;

            if (_options.ApiQueryURL is not null)
            {
                doc = await _httpService.GetXmlResponseAsync(_options.ApiQueryURL);

                if (doc.Nodes().Any())
                {
                    devices = GetDevices(doc);
                    await _dataService.UpdateDevicesAsync(devices);
                }
            }
        }
        catch (Exception ex)
        {
            if (OperatingSystem.IsWindows() && _eventLog != null)
            {
                _eventLog.WriteEntry($"Error occurred: {ex.Message}", EventLogEntryType.Error);
            }
        }

        await Task.Delay(TimeSpan.FromHours(1), stoppingToken);
    }
}

private bool PrerequisitesMet()
{
    // options
    if (_options == null)
        return false;

    // option "ApiQueryURL"
    if (string.IsNullOrWhiteSpace(_options.ApiQueryURL))
        return false;

    // option "TargetString"
    if (string.IsNullOrWhiteSpace(_options.TargetString))
        return false;

    return true;
}