Gravatar URI fallback extension.

gravatar.cs

public static class AvatarUriExtensions
{
    public static string GetAvatarUri(this User user)
    {
        return GetAvatarUri(user.AvatarUri, user.Email);
    }

    /// <summary>
    /// Returns the uri or the Gravatar address as a fallback.
    /// </summary>
    /// <param name="uri">the avatar uri</param>
    /// <param name="email">the email address which is used for the fallback.</param>
    /// <returns></returns>
    private static string GetAvatarUri(string uri, string email)
    {
        return !string.IsNullOrEmpty(uri) ? uri : new Gravatar.UriBuilder(new HashProvider()).CreateAddress(email);
    }
}