Aggregation type parameters should have defaults

[tajakobsen]

The recent changes in contentLib and nodeLib forces a developer to specify Aggregation type parameters when using the parameter and result interfaces for query() et al.

By adding some default type parameters the developers would not need to deal with missing Aggregation type parameters if they are not needed anyway.

-function getById(id: string): ContentsResult<ContentArticle, never> { ... }
+function getById(id: string): ContentsResult<ContentArticle> { ... }