Description:
------------
pg_query_params modifies null values in array to empty strings.

(similar, but different to bug #36606, I can verify that #36606 is fixed for me!)


Reproduce code:
---------------
// createdb saga3; 
// echo 'CREATE TABLE pais (idpais integer);' | psql saga3

$a = pg_connect("dbname=saga3");
$b = array(null);
var_dump($b); 
pg_query_params($a, "SELECT * FROM pais WHERE idpais = $1", $b);
var_dump($b); 
die;

Expected result:
----------------
array(1) {
  [0]=>
  NULL
}
array(1) {
  [0]=>
  NULL
}

Actual result:
--------------
array(1) {
  [0]=>
  NULL
}
array(1) {
  [0]=>
  string(0) ""
}