[已解决]VBS的if语句怎样判断空变量？

dim ws,fs,current_path_files,current_path_subfolders,att,files_sum,subfolders_sum
'on error resume next

set ws=wscript.createobject("wscript.shell")
set fs=wscript.createobject("scripting.filesystemobject")

set current_path_files=fs.getfolder(ws.CurrentDirectory).files
set current_path_subfolders=fs.getfolder(ws.CurrentDirectory).subfolders
'==========================================================================
for each file in current_path_files
  'ignore the shortcut and link
  att=file.attributes
  if att=4+2 or att=4+2+1 or att=4+2+32 or att=4+2+32+1 then
    files_sum=files_sum & file.name & vbnewline
  end if
next

for each subfolder in current_path_subfolders
  'ignore the shortcut and link
  att=subfolder.attributes
  if att=4+2 or att=4+2+16 or att=4+2+16+1 then
    subfolders_sum=subfolders_sum & subfolder.name & vbnewline
  end if
next
'==========================================================================
if files_sum <> "" then
  msgbox files_sum,,"Exist Hide and System file(s):"
end if

if subfolders_sum <> "" then
  msgbox subfolders_sum,,"Exist Hide and System folder(s):"
end if
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