With XAF v17.1, Solution Wizard sets the XafApplication.OptimizedControllersCreation property to True for newly created XAF projects (existing projects will not be affected). 

To avoid possible null reference exceptions in nested List Views, always check if the Frame.GetController<ControllerType> method result is not null when the OptimizedControllersCreation property is true. The latter option is required to get faster loading of DetailView when it contains a lot of nested ListView items (learn more...).

Our online documentation was already updated to describe this optimization specificity and add these null-checks everywhere; e.g., check theses examples: one, two. KB articles, Code Examples and popular Support Center tickets are not yet updated, but we hope to do this with time as well. Should you find missing checks in our learning materials, please contact us.