I did some tests, and I am not sure if this is not bug:
postgres=# select '{"x":20}'::jsonb - 'x'::text; ERROR: unknown type of jsonb container --->>> it should be empty jsonb, not error Time: 0.971 ms postgres=# select '{"x":20, "y":30}'::jsonb - 'x'::text; ┌───────────┐ │ ?column? │ ╞═══════════╡ │ {"y": 30} │ └───────────┘ (1 row)
Some of this logic needs tightening. The attached patch should do that. Among other things, it errors out if we attempt to delete or replace on a scalar, just returns the input argument if there are no changes instead of cloning it, checks via an Assert that the constructed JsonbValue is not null, and otherwise returns it unconditionally. The result is actually simpler code, I think. Before I apply it I'd like to have comments from Dmitry and Petr, just to make sure I haven't inadvertently slipped my moorings.
