It would seem that if I define a field for a feature with null values not allowed and host the features in AGOL, Collector populates this (with a space when it's a text field, for example) so the collector can submit without typing anything.. so it sort of defeats the point of not allowing null values. Thoughts?
I've passed this one on to Esri as I noticed some related weirdness across AGOL and Collector including..
Collector / AGOL - Drop-down fields that don’t allow null values can be left unselected
AGOL - Drop-down fields that should allow null values are marked as “this value is required”
AGOL - Auto-populating fields that don't allow null values so the user can submit without typing anything (like Collector), but also letting you remove the auto-added character and storing the feature with no value for the field