Query on pg_settings view

Hi,

I have a weird case when running a query on the pg_settings view.
I have two users, first one is the default user - postgres which is a
superuser and another one is a role which i had created, i called it
test_role and it's not a superuser.
When I run a select on pg_settings with these two users I recieve different
results.
Running the query 'select * from pg_settings' with 'postgres' user returns
269 rows when running the same query with 'test_role' returns 254 rows.
For example, the following query 'select lower(setting) from pg_settings
where lower(name) = 'config_file'' returns null when I connect with
'test_role' but with 'postgres' user I recieve one row
(/var/lib/pgsql/9.6/data/postgresql.conf).

I have granted all privileges on pg_settings to 'test_role' but it didn't
changed the results.

I don't have any idea what it's wrong here.

The PostgreSQL version is PostgreSQL 9.6.1 on x86_64-pc-linux-gnu

Can you please help me with this issue?

Thanks in advance,
Ronen