BUG #14494: Regression - Null arrays are not queryable

The following bug has been logged on the website:

Bug reference: 14494
Logged by: Linas Vepstas
Email address: linasvepstas(at)gmail(dot)com
PostgreSQL version: 9.6.1
Operating system: Debian unstable
Description:

Array handling appears to have regressed,
with lots of surprising results for empty
and null arrays.

CREATE TABLE foo (
name TEXT,
outgoing BIGINT[]
);

INSERT INTO FOO VALUES ('one', '{43, 67}');
INSERT INTO FOO VALUES ('two', '{}');
INSERT INTO FOO VALUES ('three', null);

test=> select * from foo;
name | outgoing
-------+----------
one | {43,67}
two | {}
three |
(3 rows)

very good!

test=> select * from foo where outgoing='{}';
name | outgoing
------+----------
two | {}
(1 row)

very good!

test=> select * from foo where outgoing=null;
name | outgoing
------+----------
(0 rows)

unexpected: wanted one row here.

test=> select * from foo where outgoing != '{43,67}';
name | outgoing
------+----------
two | {}
(1 row)

unexpected: wanted two rows here. Where did the null row go?
test=> select * from foo where array_length(outgoing,1)=2 ;
name | outgoing
------+----------
one | {43,67}
(1 row)

very good

test=> select * from foo where array_length(outgoing,1)=0 ;
name | outgoing
------+----------
(0 rows)

Huh? there is at least one array whose length is zero, and another that
doesn't have a length...