log4net archiving on log rotation

CustomRollingFileAppender.cs

 public class CustomRollingFileAppender : RollingFileAppender
    {
        private static readonly log4net.ILog Logger = log4net.LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);


        protected override void AdjustFileBeforeAppend()
        {          
            var previousFile = File; 
            base.AdjustFileBeforeAppend();
            if (File != previousFile)
            {
                try
                {
                    FileInfo fa = new FileInfo(previousFile);
                    if (System.IO.File.Exists(fa.FullName + ".zip"))
                    {

                        using (ZipArchive zip = ZipFile.Open(fa.FullName + ".zip", ZipArchiveMode.Update))
                        {
                            if (zip.Entries != null && zip.Entries.Count > 0)
                            {
                                zip.CreateEntryFromFile(fa.FullName, fa.Name + "." + zip.Entries.Count.ToString());
                            }
                            else
                            {
                                zip.CreateEntryFromFile(fa.FullName, fa.Name);
                            }
                        }
                    }
                    else
                    {
                        using (ZipArchive zip = ZipFile.Open(fa.FullName + ".zip", ZipArchiveMode.Create))
                        {
                            zip.CreateEntryFromFile(fa.FullName, fa.Name);
                        }
                    }
                    System.IO.File.Delete(fa.FullName);
                }
                catch (Exception ex)
                {
                    Logger.Fatal("Error While archiving Zip File :" + ex.Message);
                }
            }
           
        }
    }