Given the following, minimal sample:
Summary: No result is returned if a constant without aggregate function is selected and a HAVING clause (with a constant expression like 'TRUE'), without an explicit GROUP BY clause is used on an empty table.
I expect that a single 1 is returned. This is also the behaviour of Postgres and described here (https://stackoverflow.com/a/53238082). The HAVING groups the empty result into a single, but existing group. HAVING doesn't filter this single row, so a single row and result should be returned.
When a explicit GROUP BY is used, or COUNT ( * ) is used additionally, or there exists an entry in the table, a 1 is returned, which is correct.