Default database not picked for pg:psql when --credential passed in

[msakrejda]

maciek@mothra:~$ <<<"select 1" heroku pg:psql -a creds-testing
--> Connecting to postgresql-tetrahedral-77884
Pager usage is off.
Null display is "💩".
 ?column? 
----------
        1
(1 row)

maciek@mothra:~$ <<<"select 1" heroku pg:psql --credential read-only -a creds-testing
 ▸    Couldn't find that addon.
maciek@mothra:~$ <<<"select 1" heroku pg:psql --credential read-only postgresql-tetrahedral-77884 -a creds-testing
--> Connecting to postgresql-tetrahedral-77884
Pager usage is off.
Null display is "💩".
 ?column? 
----------
        1
(1 row)