Updating transient to remove expiration fails

[stndrdsnz]

When updating a transient using the set_transient method, it fails to update the transient's expiration date.

Looking at the code, it appears it's only looking for the expiration and deleting it if a new expiration date is specified. This renders it impossible to switch a transient from having an expiration date to not having one.

ex. code:

<?php
//new transient set to expire in one hour
set_transient('new_transient', 'data', 5000);

//Update transient and remove expiration
set_transient('new_transient', 'new_data', 0);

At this point, if you look in the options table for the _transient_new_transient_expiration you'll find the previous value of 1 hour for the expiration instead of the expiration having been removed.

One thing I recognize, that may render this from being a "bug" is the nature of transients would be if transient information isn't available, it shouldn't be relied upon, but rather rebuilt. In this use case above, a transient that's set to not expire, but actually still has an expiration date, would expire and in theory then be regenerated later if the data is requested after the expiration.