-- null scalar
SELECT r, pg_typeof(r) FROM (SELECT vec_coalesce(ARRAY[1,2,3]::integer[], NULL)) r(r);
 r | pg_typeof 
---+-----------
   | integer[]
(1 row)

-- ints
SELECT r, pg_typeof(r) FROM (SELECT vec_coalesce(ints, 0) FROM measurements WHERE sensor_id BETWEEN 1 AND 5) r(r);
    r    | pg_typeof 
---------+-----------
         | integer[]
 {0,0,0} | integer[]
 {1,2,3} | integer[]
 {1,0,2} | integer[]
 {1,2,4} | integer[]
(5 rows)

-- floats
SELECT r, pg_typeof(r) FROM (SELECT vec_coalesce(floats, 0) FROM measurements WHERE sensor_id BETWEEN 1 AND 5) r(r);
    r    |     pg_typeof      
---------+--------------------
         | double precision[]
 {0,0,0} | double precision[]
 {1,2,3} | double precision[]
 {1,0,2} | double precision[]
 {1,2,4} | double precision[]
(5 rows)

--numeric
SELECT r, pg_typeof(r) FROM (SELECT vec_coalesce(nums, 0) FROM measurements WHERE sensor_id BETWEEN 1 AND 5) r(r);
        r         | pg_typeof 
------------------+-----------
                  | numeric[]
 {0,0,0}          | numeric[]
 {1.23,2.34,3.45} | numeric[]
 {1.23,0,2.34}    | numeric[]
 {1.23,2.34,4.45} | numeric[]
(5 rows)