Returning Void Type in Mutations with SmallRye GraphQL

While by default MicroProfile GraphQL specification doesn't provide direct support for returning void type from mutation operations, SmallRye GraphQL has implemented this feature based on user feedback.

To implement a mutation operation that returns void or Void type, you can use the following pattern in your annotated @GraphQLApi class:

    @Mutation
    public void createHero(SuperHero hero) {
        superHeroService.create(hero);
    }

In this example, createHero() receives a SuperHero object as input, performs some operation with it (in this case, creating it using a superHeroService).

[NOTE] On the GraphQL level, this is achieved by returning a special scalar type named Void from the mutation. This scalar type will always have a value of null.