BUG #15140: Incorrect jsonb_set behavoir

The following bug has been logged on the website:

Bug reference: 15140
Logged by: Ivan Panchenko
Email address: i(dot)panchenko(at)postgrespro(dot)ru
PostgreSQL version: 10.3
Operating system: any
Description:

First. Impossible to create a nested structure for a path with more than one
new keys.

postgres => select jsonb_set('{}'::jsonb, array['x', 'y'],
to_jsonb(1::text), true);
jsonb_set
-----------
{}
(1 строка)

Expected {"x": { "y" : "1" }}

Second. Setting a NULL value nullifies the whole JSON

postgres=> select jsonb_set('{}'::jsonb, array['x'], null, true);
jsonb_insert
--------------

(1 строка)

Expected { "x" : null }