Description:
------------
PDO contructer return null and output warning() when given unexpected type arguments.
I think it is better that throw PDO exception with relevant message or update PHPDoc to indicate this specification.

How about that?

Test script:
---------------
<?php

try {
    $pdo = new PDO('pgsql:host=db;dbname=hoge', 'postgres', [], []);
    var_dump(is_null($pdo));
} catch(PDOException $e) {
    var_dump($e->getMessage());
}


Expected result:
----------------
string(64) "PDO::__construct() expects parameter 3 to be string, array given"

Actual result:
--------------
Warning: PDO::__construct() expects parameter 3 to be string, array given in /Users/kazushige.tominaga/test-prestissimo/hoge.php on line 2
bool(true)