BUG #4613: intarray_del_elem returns an invalid empty array (for nullif comparison)

The following bug has been logged online:

Bug reference:      4613
Logged by:          Valentine Gogichashvili
Email address:      valgog@gmail.com
PostgreSQL version: 8.3.1
Operating system:   Debian Linux  (kernel 2.6.8)
Description:        intarray_del_elem returns an invalid empty array (for
nullif comparison)
Details:

I have checked the issue on the 8.2.1 and 8.3.1 by now.

When contrib/intarray module - operation (intarray_del_elem) returns an
empty array, is not supposed to be empty

testdb=# select

'{ -1 }'::integer[] - ( -1 ) as calculated_empty_int_array,

nullif( '{ -1 }'::integer[] - ( -1 ), '{}'::integer[]) as should_be_null,

nullif( '{}'::integer[], '{}'::integer[]) as
works_for_initially_empty_array,

nullif( '{ }'::integer[] - ( -1 ), '{}'::integer[]) as also_works;

 calculated_empty_int_array | should_be_null |
works_for_initially_empty_array | also_works
----------------------------+----------------+------------------------------
---+------------
 {}                         | {}             |
  |
(1 row)

So if we try to nullif an empty array, that was generated by the - operator
'{-1}'::integer[] - (-1), it does not see the array is empty.

With best regards,

-- Valentine Gogichashvili