Description:
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On linux, this code runs perfectly fine and as expected, on windows, it seems that session_write is not called at all or given null params.

Reproduce code:
---------------
<?php
session_set_save_handler('var_dump','var_dump','var_dump','var_dump','var_dump','var_dump');
session_start();
$_SESSION['foo'] = "bar";
$_SESSION = array_merge($_SESSION,array('foo'=>'foo','bar'=>'bar'));
session_write_close();
var_dump($_SESSION);
?>

Expected result:
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Warning: Wrong parameter count for var_dump (i believe triggered by session_close callback) and a dump of the session id and serialized session data.  On both the expected and non-expected results, var_dump shows the expected array structure.

Actual result:
--------------
1 wrong parameter count for var_dump given by the session close callback, and nothing else concerning session write callback.  However, the var_dump of $_SESSION shows the correct array structure.