PAM_AUTHENTICATE fails when password is empty.

Hi there,

I have a problem regarding PAM.
I wrote a function to change a user-password. That function checks the
current password by using "pam_authenticate" and it works very well so
far. But if a user has no password set and wants to do it now,
pam_authenticate fails and so my function fails. Pam_authenticate
seems to work only if the authenticating user has a password - but
why?
So I need an alternative to pam_authenticate or a possibility to
check, whether the password is NULL or not.

Thanks for your support!

Phil