/// <summary>
/// Adds and converts a card to the attachments list.
/// </summary>
/// <param name="attachments">A list of attachments.</param>
/// <param name="card">The card.</param>
public static void Add(this IList <Attachment> attachments, SigninCard card)
{
attachments.ThrowIfNull(nameof(attachments));
card.ThrowIfNull(nameof(card));
attachments.Add(card.ToAttachment());
}