Insert NULL instead of empty string with PDO

If you want null, just insert null instead of empty string.

$stmt2->bindParam(':title', $title === '' ? null : $title, PDO::PARAM_STR);

Besides xdazz's more appropriate answer, you can often solve something like this in SQL: Just rephrase the query INSERT INTO ... VALUES (?) to something like INSERT INTO ... VALUES (NULLIF(?, '')).