VixHost_Connect fail with NULL username and password

I'm working on VMware Server 2.0. In Vix API document, it says that if you want to connect to localost with current login, then you can use NULL for hostname, username and password. I just want so. But when I use NULL for host name, VixHost_Connect fails with error message:

18002 Malformed hostname parameter.  For the given service provider, the hostname must be a URL, in the form https://<hostname>:<port>/sdk

I have to change host name to https://127.0.0.1:8333/skd. But this is ok for me. All I want is to use NULL for user name and password, because I don't want to hardcode root's password in my program.

But when I use NULL for user name and password, I get error message:

1 Unknown error

What's the problem? How to solve it?

Thanks in advance!