Description:
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Using PDO::PARAM_NULL when doing a bindParam()/bindValue() does not insert a NULL value. It appears to insert the default value instead. '' in (var)char/text fields, 0 in boolean fields, ect.

Reproduce code:
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$stmt = 'INSERT INTO table (field) VALUES (:placeholder)';
$stmt->bindValue(':placeholder', PDO::PARAM_NULL);
$stmt->execute();

Expected result:
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`field` in `table` set to NULL

Actual result:
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`field` in `table` set to default value