public IEnumerable <Label> AddLabels(Topic topic, ImageLabel image, IEnumerable <Label> labels)
{
#region validation
if (topic == null)
{
throw new ArgumentNullException(nameof(topic));
}
if (image == null)
{
throw new ArgumentNullException(nameof(image));
}
if (labels == null)
{
throw new ArgumentNullException(nameof(labels));
}
#endregion
image.Labels = LabelRepository.AddLabels(topic, image, labels).ToList();
return(image.Labels ?? new List <Label>());
}