Description:
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Fetching data on BIT columns with NULL values return 0 (zero) instead of NULL.

Reproduce code:
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<?php
$db = new PDO('dblib:host=X;dbname=X', 'x', 'x');
print_r($db->query("SELECT CONVERT(BIT,NULL) AS THIS_MUST_BE_BLANK")->fetch(PDO::FETCH_ASSOC));

Expected result:
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Array ( [THIS_MUST_BE_BLANK] =>  )

Actual result:
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Array ( [THIS_MUST_BE_BLANK] => 0 )