Does PostgreSQL index null values?
Since at least PostgreSQL 8.3, PostgreSQL indexes NULL using a bitmap on the index. That means "yes" it's indexed. Except it takes a bit, rather than a byte[s]. There is no speed advantage insofar as btree indexes are concerned with using a non-NULL value. It will work just as you'd expect.

Dragons here: for more information see this,


http://patshaughnessy.net/2014/11/11/discovering-the-computer-science-behind-postgres-indexes