Add less verbose ways to say that types are not nullable by default

[gilberto-torrezan]

With the introduction of V21, parameter types and return types from endpoints are now nullable by default. Making an type not-nullable when accessed via TypeScript requires the use of an "@nonnull" annotation.

The problem is: in order to make the Typescript calls cleaner, every single attribute or return type needs to be annotated with @Nonnull, which becomes quite verbose. Also when using Lists, annotating parameterized types is not convenient (some IDEs have poor support for such structure). Example: @Nonnull List<@Nonnull Person>.

There should be an easier way for the developers to say that either all Endpoints or some subset of Endpoints have all types not-nullable (basically the behavior up to V20).

This can be done in the following ways:

• Introduce a class level @Nonnull annotation, that makes all types declared in the methods of the class @Nonnull by default;
• Introduce a configuration flag in the pom.xml to make all Endpoints @Nonnull by default (the behavior from V20);
• Having a separate configuration file with types that are always @Nonnull (or the opposite, a list with only nullables).

We are open to feedback on which solution would be the best (or other solutions as well).

[Artur-]

I think we should avoid a global configuration flag because this would mean that you no longer can understand how an endpoint class works by looking at it and its parent class.

[knoobie]

Spring (fusion already depends on it) has already a quite good (and IDE supported) way of reducing boilerplate with the specific annotations for fields and apis - see https://www.baeldung.com/spring-null-safety-annotations for more informations.

[haijian-vaadin]

thanks for the suggestion @knoobie, we decided to go with the package level annotation for nonnullable.