Hello,
Cisco Configuration Professional is very limited, I don't think it will let you enter a blank password at all.
Below is what the dialer interface should look like. Try and get to the command line, you can then just configure the CHAP username:
interface Dialer0
description ADSL_DIALER
ip address negotiated
ip mtu 1432
encapsulation ppp
dialer pool 1
dialer-group 1
tcp adjust-mss 1392
ppp authentication chap pap callin
ppp chap hostname USERNAME