diff --git a/lib/resty/upload.lua b/lib/resty/upload.lua
index c10a74e..0c8072a 100644
--- a/lib/resty/upload.lua
+++ b/lib/resty/upload.lua
@@ -3,7 +3,6 @@
 
 local sub = string.sub
 local req_socket = ngx.req.socket
-local null = ngx.null
 local match = string.match
 local setmetatable = setmetatable
 local error = error