This query returns null and not an empty string but that’s not really evident in psql.
postgres=# SELECT to_char('1997-02-28 10:30:00'::TIMESTAMP, null);
to_char
---------
(1 row)
To change this behaviour, set this configuration
postgres=# \pset null null
Null display is "null".
Context:
I was working on https://github.com/apache/arrow-datafusion/pull/9689 and just assumed that the value being returned was an empty string since I didn’t see anything when I ran the above SELECT query in psql. I should’ve verified my assumption like this:
SELECT
CASE
WHEN your_column IS NULL THEN 'Value is NULL'
ELSE 'Value is not NULL'
END;