Deal with NULL in Postgres

SUM up some values with NULL in it, we get a value.

WITH base AS (
    SELECT
        1 AS num
    UNION ALL
    SELECT
        2 AS num
    UNION ALL
    SELECT
        NULL AS num
)
SELECT
    SUM(num)
FROM
    base

gives us

3

However, if one would add some values up, we get a NULL when one of them is NULL.

SELECT
NULL + 10 AS null_plus_num

gives us a

NULL