Wrong result for comparing ROW(...) with IS NOT NULL

Hi,

when I do the following on PG 12.4, I get some unexpected results:

SELECT
ROW() IS NULL, -- true
ROW() IS NOT NULL; -- true

Both return true here. In any case IS NULL should return the opposite
from IS NOT NULL, right?

The same happens here:

SELECT
ROW(NULL, NULL) IS NULL, -- returns: true (expected)
ROW(NULL, NULL) IS NOT NULL, -- returns: false (expected)
ROW(1, NULL) IS NULL, -- returns: false (expected)
ROW(1, NULL) IS NOT NULL, -- returns: false !!
ROW(1, 1) IS NULL, -- returns: false (expected)
ROW(1, 1) IS NOT NULL; -- returns: true (expected)

The docs[1] say:

> Also, it is possible to [...] test a row with IS NULL or IS NOT NULL,
for example:
> [...]
> SELECT ROW(table.*) IS NULL FROM table; -- detect all-null rows

So I would expect the ROW(1, NULL) IS NOT NULL to be true, because it's
not "all-null". I'm not sure what I would expect ROW() to be, but surely
not the same for IS NULL and IS NOT NULL.

Best

Wolfgang

[1]:
https://www.postgresql.org/docs/current/sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS