`setquota': curbytes is not struct member (NameError)

[y-okubo]

I have run the following script.

#/usr/bin/env ruby
require 'quota'

DEV = '/Volumes/Quota'
QUOTA_USER = '/Volumes/Quota/.quota.user'

Quota.quotaon(DEV, QUOTA_USER)
dq = Quota.getquota(DEV, 501)
# puts dq

dq = Quota::DiskQuota.new
puts dq
dq.bsoftlimit = 100
Quota.setquota(DEV, 501, dq)
Quota.sync(DEV)

However, an error such as the title has occurred.
The system is Ruby 2.1.0p0 in Mac OS X 10.9.1!