Where is workbook:Close()

<pre>
local filename = "C:\\Users\\Administrator\\Desktop\\test.xlsx"  --normal and existing excel file, contains 1 sheet
local xlsx = require 'xlsx' 
local workbook = xlsx.Workbook(filename)
print("total sheets=" .. workbook:GetTotalWorksheets())  --print 1 , OK
workbook:Close() -- ERROR: attempt to call method 'Close' (a nil value)
</pre>
 

workbook:Close() got removed ?
