That's probably not what he meant. ioFTPD expects at least one character as password when the client sends the "PASS xxx\r\n" command. If u want a user to login with any (non-zero-length) password, u can give him the A flag. But "PASS \r\n" will not work by design.
Code:
> 220 ioFTPD v5.8.5 ready.
USER xyz
> 331 Password required for xyz.
PASS
> 501 'PASS': Not enough parameters.