Attempt to index local 'form' (a nil value)

Hi,
I am following below code on fedora Linux with nginx:

        local resty_sha256 = require "resty.sha256"
        local upload = require "resty.upload"

        local chunk_size = 4096
        local form = upload:new(chunk_size)
        local sha256 = resty_sha256:new()
        local file

        local upload_path = '/tmp/uploads/'


        while true do
           local typ, res, err = form:read()

            if not typ then
                ngx.say("failed to read: ", err)
                return
            end

            if typ == "header" then
                local file_name = upload_path .. ngx.time()
                if file_name then
                    file = io.open(file_name, 'w+')
                    if not file then
                        ngx.say("failed to open file ", file_name)
                        return
                    end
                end
            elseif typ == "body" then
                if file then
                    file:write(res)
                    sha256:update(res)
                end
            elseif typ == "part_end" then
                file:close()
                file = nil
            elseif typ == "eof" then
                break
            else
                -- nothing
            end
        end

        local digest = sha256:final()
        sha256:reset()

        local str = require "resty.string"
        ngx.say("sha256: ", str.to_hex(digest))```

When I run this as

curl -F "filename=@shatest.lua" http://127.0.0.1:8089/uploadtest

It gives me below errors:

$ tail -f /usr/local/openresty/nginx/logs/error.log 2016/06/29 15:26:23 [error] 31449#0: *12 lua entry thread aborted: runtime error: /usr/local/openresty/nginx/uploadtest.lua:13: attempt to index local 'form' (a nil value) stack traceback: coroutine 0: /usr/local/openresty/nginx/uploadtest.lua: in function </usr/local/openresty/nginx/uploadtest.lua:1>, client: 127.0.0.1, server: localhost, request: "POST /uploadtest HTTP/1.1", host: "127.0.0.1:8089"

Can you please help me what is wrong here?

Reproduce the report using uploadtest.lua, the shown curl command, and the Fedora/nginx setup. Start at line 13 where form:read() is called and inspect how resty.upload is required and initialized; done means identifying why form is nil and documenting a verified resolution.