https://linear.app/unleash/issue/SR-169/ticket-1107-project-feature-flag-limit-is-not-correctly-updatedFixes#5315, an issue where it would not be possible to set an empty
flag limit.
This also fixes the UI behavior: Before, when the flag limit field was
emptied, it would disappear from the UI.
I'm a bit unsure of the original intent of the `(data.defaultStickiness
!== undefined || data.featureLimit !== undefined)` condition. We're in
an update method, triggered by a PUT endpoint - I think it's safe to
assume that we'll always want to set these values to whatever they come
as, we just need to convert them to `null` in case they are not present
(i.e. `undefined`).
15f77f5b8b