AuthDatabase CheckPassword broken?

[Mark Foley]

I had been using the CheckPassword authentication interface with dovecot 2.2.15, 
https://wiki2.dovecot.org/AuthDatabase/CheckPassword, and it was working.

After upgrading to 2.2.33.2 CheckPassword no longer works. The referenced wiki page says, 

Checkpassword Interface

    Read <username> NUL <password> NUL from fd 3. 

I've checked the information read from fd 3 with 2.2.33.2 and I get <username> followed by 3
nulls. I'm guessing the 2nd null is supposed to be the password.

Why is this no longer working? How can I fix it?

THX --Mark