How to publish changes in the vShield spoofguard with REST API?

Hi

I'm working with vShield 5.1 and in the P187 of <<vShield API Programming Guide>>,"Change SpoofGuard IP Settings",It says that "If the action is publish then no message body is required".So I use the URL"POST https://<vsm-ip>/api/2.0/services/spoofguard/<contextID>?action = publish" ,and the post data is null. But i got a HTTP 500 error,and the error detail is "input contained no data". How to figure out this problem?