Looks like a cut-paste error, and I am a bit surpirsed that the J-series did not catch it..
Enter in configuration mode, then do:
set system login user admin authentication plain-text-password
...and press return.
The system will prompt you for a password twice; enter your password.
Then, the system will encrypt your plain-text password on the fly.
If you then do a
show system login user admin
your password should be encrypted.
(It is a bit of a lazy Friday for me..)
Saverio