Incorrect repository method return type

Reports incorrect Micronaut Data repository method return types.

The following return types are supported:

• void

• Primitive types

• Simple types

• java.util.List or any common Iterable type

• java.util.stream.Stream

• java.util.Optional

• io.micronaut.data.model.Page

• io.micronaut.data.model.Slice

• java.util.concurrent.Future or java.util.concurrent.CompletableFuture

• A Reactive Streams compatible type, such as Publisher, Single, Maybe, Flux, Mono, and so on