Micronaut Data Repository Method Return Types errors.
Supported Return Types for Finder Methods

Return type	Description
`List<T>`	A java.util.List or any common Iterable type
`Stream<T>`	A Java 8 java.util.stream.Stream instance
`Optional<T>`	An optional value, if null is retrieved otherwise a EmptyResultException is thrown
`Page<T>`	An instance of io.micronaut.data.model.Page for pagination.
`Slice<T>`	An instance of io.micronaut.data.model.Slice for pagination.
`Future<T> or CompletableFuture<T>`	A java.util.concurrent.Future for asynchronous execution
`Publisher<T> (or Single, Maybe, Flux, Mono etc.)`	An Reactive Streams compatible type
`Primitive/Simple Types`	In the case of projections primitive/basic types can be returned