Postgresql will print out an error:
user error (key "port" not present)
We should be using a default port. But also we should be using file-location or some technique so that the user knows the error is occurring in Persistent.
FWIW, this error happens in persistent-mysql as well.
I've opened an issue with aeson: bos/aeson#104.
I'll implement the default port now.
PostgreSQL default port (#60)
waiting on a new release of aeson
aeson released modifyFailure now.
I don't think this is implemented yet.