What's the proper way to test if a Postgresql array field is either null or empty

Question

I have a table defined with an integer_array field. It contains the following data:

 id | black_list 
----+------------
  4 |            
  5 |            
  8 |            
 12 |            
  6 |            
  7 |            
 10 | {5}        
 13 | {5}        
  3 | {}         
  9 | {3}        
 11 | {}         
 14 | {}         
  1 | {}         
  2 | {}         
 15 | {}         
 16 | {}         
 17 | {}         
(17 rows)

I need to write a query to see if the array field is empty - NULL or otherwise. The trouble is that the {} values are not null, nor do they return any length from the ARRAY_LENGTH function. None of the other array functions listed at http://www.postgresql.org/docs/8.4/static/functions-array.html seem to be what I need either. I've found that I can write ARRAY_LENGTH(0 || black_list) to get all of them to return a length of 1 or more, but that seems like a nasty hack. What's the proper way to test this?

Bonus question: What exactly is {} representative of? I've been unable to write a select statement that will return that value. ARRAY[] throws an error, ARRAY[""] returns {""}, ARRAY[NULL] returns {NULL}, etc.

Answer 1

{} seems to represent an empty array, which would explain both the value being NOT NULL and ARRAY_LENGTH({}) not returning anything – though I'd expect it to return 0 on {}, perhaps that's a PostgreSQL peculiarity with which I'm unfamiliar.

Is there a reason you can't just test the return value of ARRAY_LENGTH, as e.g.

SELECT id FROM table WHERE ARRAY_LENGTH(black_list, 1) IS NULL OR ARRAY_LENGTH(black_list, 1) < 1

Assuming ARRAY_LENGTH() doesn't lose its mind on empty values such as that for id=12 in the example above, it seems like that'd do the trick.