Suite: Add nullable annotation to manager methods and entity ctor #15301
Description
Resolves #15298
Checklist
- I fully tested it as developer / designer and created unit / integration tests
- I documented it (or no need to document or I will create a separate documentation issue)
- I worked with the design team to get their idea for UI/UX design (or no need to design for this PR)
- I've assigned reviewer, related labels and set a milestone for this PR
How to test it?
Create a project via Suite, generate CRUD pages (set some properties as nullable and set some string properties as not required) with Navigation Connections & Properties, and then check the related domain service methods and entities.