PostgreSQL - using password/md5 authentication with empty password
Indeed an empty password is equivalent to no password so it's not going to be accepted by the server when pg_hba.conf says that a password is required.

Still, there are various ways to avoid inputting the password:


trust method in pg_hba.conf, possibly constrained to a specific user and database
client-side PGPASSWORD environment variable
client-side .pgpass file
dummy password like "test" stored in the same place than the login name