Persist bombs out when form changes or there is no default value.

[GantMan]

It appears using persist requires a default to be set, and is quite temperamental with App persistent data.

e.g. Adding a switch, and not having a default value causes the form to normally be fine. But with persist turned on it's a bit more sensitive and bombs the app out.

Similarly, adding a new field when persist is in place, will require a simulator reset. I believe these two are associated in some way.

I will attempt to figure out and fix with a PR when I have free time.

[drewhamlett]

Hey just noticed this too. Would be good if we could have a blank field. Right now I'm having to set a 0 for all fields, which looks kind of ugly.