no password on postgres user and pgagent

Hello,

I'd like to run pgagent with the postgres user, which doesn't have a
password.  I thought it'd be as simple as setting up an init script as:

[ -- Begin <pgagent_start.sh> ---------------------------------------------- ]
#! /bin/sh

pgagent user=postgres host=localhost dbname=postgres
[ -- End <pgagent_start.sh> ------------------------------------------------ ]

and then the following should work:

---<--------------------cut here---------------start------------------->---
$ sudo -u postgres sh pgagent_start.sh
sluque@otaria:~$ Mon May  9 16:23:00 2016 : WARNING: Couldn't create the primary connection (attempt 1): fe_sendauth:
nopassword supplied 
Mon May  9 16:23:05 2016 : WARNING: Couldn't create the primary connection (attempt 2): fe_sendauth: no password
supplied
Mon May  9 16:23:10 2016 : WARNING: Couldn't create the primary connection (attempt 3): fe_sendauth: no password
supplied
Mon May  9 16:23:15 2016 : WARNING: Couldn't create the primary connection (attempt 4): fe_sendauth: no password
supplied
Mon May  9 16:23:20 2016 : WARNING: Couldn't create the primary connection (attempt 5): fe_sendauth: no password
supplied
Mon May  9 16:23:25 2016 : WARNING: Couldn't create the primary connection (attempt 6): fe_sendauth: no password
supplied
Mon May  9 16:23:30 2016 : WARNING: Couldn't create the primary connection (attempt 7): fe_sendauth: no password
supplied
Mon May  9 16:23:35 2016 : WARNING: Couldn't create the primary connection (attempt 8): fe_sendauth: no password
supplied
Mon May  9 16:23:40 2016 : WARNING: Couldn't create the primary connection (attempt 9): fe_sendauth: no password
supplied
Mon May  9 16:23:45 2016 : WARNING: Couldn't create the primary connection (attempt 10): fe_sendauth: no password
supplied
Mon May  9 16:23:45 2016 : ERROR: Stopping pgAgent: Couldn't establish the primary connection with the database server.
---<--------------------cut here---------------end--------------------->---

Does one *have* to supply a password for postgres?

Thanks,

--
Seb