ICSharpCode.SharpZipLib.Zip.ZipFile.AddDirectory C# (CSharp) Method

        public void AddDirectory(string directoryName) {
            if (directoryName==null) {
                throw new ArgumentNullException("directoryName");
            }

            CheckUpdating();

            ZipEntry dirEntry=EntryFactory.MakeDirectoryEntry(directoryName);
            AddUpdate(new ZipUpdate(UpdateCommand.Add, dirEntry));
        }

 /// <summary>
 /// Iterate thru all the filesysteminfo objects and add it to our zip file
 /// </summary>
 /// <param name="fileSystemInfosToZip">a collection of files/directores</param>
 /// <param name="z">our existing ZipFile object</param>
 private static void GetFilesToZip(FileSystemInfo[] fileSystemInfosToZip, ZipFile z)
 {
     //check whether the objects are null
     if (fileSystemInfosToZip != null && z != null)
     {
         //iterate thru all the filesystem info objects
         foreach (FileSystemInfo fi in fileSystemInfosToZip)
         {
             //check if it is a directory
             if (fi is DirectoryInfo)
             {
                 DirectoryInfo di = (DirectoryInfo)fi;
                 //add the directory
                 z.AddDirectory(di.FullName);
                 //drill thru the directory to get all
                 //the files and folders inside it.
                 GetFilesToZip(di.GetFileSystemInfos(), z);
             }
             else
             {
                 //add it
                 z.Add(fi.FullName);
             }
         }
     }
 }