Description:
------------
Passing object that implement ArrayAccess interface to PDO constructor(forth 
param), the constructor will return NULL, no Exception raised.
(I‘m not sure is the bug come from PDO or ArrayAccess.)

Test script:
---------------
$config = array(...);

$options = new SomeObjImplArrAcc(); // just an empty object
$pdo = new PDO($config['dsn'],$config['user'],$config['pass'],$options);
var_dump($pdo); // <- NULL

$options[PDO::ATTR_PERSISTENT] = true; // or have some elements
$pdo = new PDO($config['dsn'],$config['user'],$config['pass'],$options);
var_dump($pdo); // <- NULL

// but success if convert to "native" array
$pdo = new PDO($config['dsn'],$config['user'],$config['pass'],(array)$options);
var_dump($pdo); // <- {PDO}[0]

Expected result:
----------------
construct three same PDO object