SELECT INTO without columns or star

Hi, hackers

When I exec a sql SELECT INTO without columns or * by mistake, it succeeds:

select * from t1;
 a | b
---+---
 1 | 2
 2 | 3
 3 | 4
(3 rows)

select into t2 from t1;
SELECT 3

 \pset null '(null)'
Null display is "(null)".

select * from t2;
--
(3 rows)

It seems that t2 has empty rows but not null. Is it an expected behavior?
And what’s the semantic of SELECT INTO without any columns?
I also see lots of that SELECT INTO in out test cases like:
-- SELECT INTO doesn't support USING
SELECT INTO tableam_tblselectinto_heap2 USING heap2 FROM tableam_tbl_heap2;

Regards,
Zhang Mingli