System.Security.Permissions.EnvironmentPermission.Union C# (CSharp) Method

        public override IPermission Union(IPermission other)
        {
            return default(IPermission);
        }

 public override IPermission Union(IPermission target)
 {
     if (target == null)
     {
         return(Copy());
     }
     else if (!(target is FileIOPermission))
     {
         throw new ArgumentException(_("Arg_PermissionMismatch"));
     }
     else if (IsUnrestricted() ||
              ((FileIOPermission)target).IsUnrestricted())
     {
         return(new FileIOPermission
                    (PermissionState.Unrestricted));
     }
     else
     {
         return(new FileIOPermission
                    (PermissionState.None,
                    EnvironmentPermission.Union(readList,
                                                ((FileIOPermission)target).readList, false),
                    EnvironmentPermission.Union(writeList,
                                                ((FileIOPermission)target).writeList, false),
                    EnvironmentPermission.Union(appendList,
                                                ((FileIOPermission)target).appendList, false),
                    EnvironmentPermission.Union(discoveryList,
                                                ((FileIOPermission)target).discoveryList, false),
                    allLocalFiles |
                    ((FileIOPermission)target).allLocalFiles,
                    allFiles | ((FileIOPermission)target).allFiles));
     }
 }