In os X it's possible to have users without passwords. If you inspect them with dscl their password show up as *. This is used for system users such as users for databases like mysql, pgsql etc. ...
I am using Mac OSX. When I type ls -l I see something like drwxr-xr-x@ 12 xonic staff 408 22 Jun 19:00 . drwxr-xr-x 9 xonic staff 306 22 Jun 19:42 .. -rwxrwxrwx@ 1 xonic staff 6148 25 ...