> That said, I think it is reasonable that a PostgreSQL JSON function
> behaves in the way that JSON users would expect, so here is my +1 for
> interpreting an SQL NULL as a JSON null in the above case
Just to chime in as another application developer: the current
functionality does seem pretty surprising and dangerous to me. Raising
an exception seems pretty annoying. Setting the key's value to a JSON
null would be fine, but I also like the idea of removing the key
entirely, since that gives you strictly more functionality: you can
always set the key to a JSON null by passing one in, if that's what
you want. But there are lots of other functions that convert SQL NULL
to JSON null:
postgres=# select row_to_json(row(null)), json_build_object('foo',
null), json_object(array['foo', null]), json_object(array['foo'],
array[null]);
row_to_json | json_build_object | json_object | json_object
-------------+-------------------+----------------+----------------
{"f1":null} | {"foo" : null} | {"foo" : null} | {"foo" : null}
(1 row)
(The jsonb variants give the same results.)
I think those functions are very similar to json_set here, and I'd
expect json_set to do what they do (i.e. convert SQL NULL to JSON
null).
Paul