Requested fields using super resource type are not taken into account

[lgringo]

When using request parameter field, if specifying a super type of the resource requested, the parameter is not taken into account.

Let's define two resources, SuperTask and SpecialTask, the latter inheriting the former, using a single repository per type hierarchy (as stated here : https://www.crnk.io/releases/stable/documentation/#_inheritance) :

`
@JsonApiResource(type = "superTasks", subTypes = SpecialTask.class)
public abstract class SuperTask {

@JsonApiId
private Long id;

private String name;

private String category;

}

@JsonApiResource(type = "specialTask", resourcePath = "superTasks")
public class SpecialTask extends SuperTask {

private boolean recurring;

private String end;

}
`
Getters and setters have been omitted for brevity.

Requesting path superTasks with request parameter, we get :

• ✔️ fields[specialTask]=name returns json including only attribute name.
• ✔️ fields[specialTask]=end returns json including only attribute end.
• ✔️ fields[specialTask]=name,end returns json including only attributes name and end.
• ❎ fields[superTasks]=namereturns json including all attributes (from SpecialTask and SuperTask).
• ❎ fields[superTasks]=name and fields[specialTask]=end returns json including only attribute end.

Expected responses :

• ✔️ fields[specialTask]=name returns json including only attribute name.
• ✔️ fields[specialTask]=end returns json including only attribute end.
• ✔️ fields[specialTask]=name,end returns json including only attributes name and end.
• ✔️ fields[superTasks]=name returns json including only attribute name.
• ✔️ fields[superTasks]=name and fields[specialTask]=end returns json including only attributes name and end.

At the moment, introducing a new type in the hierarchy (a sibling for SpecialTask) creates a breaking change for our customers, because we need them to specifiy fields for all sub-types.