r2dbc ItemController patch

ItemController.java

@RestController
@RequestMapping(value = "/items")
public class ItemController {

    private final ItemService itemService;
    private final ItemMapper itemMapper;

    ...

    @ApiOperation("Patch an existing item following the patch merge RCF (https://tools.ietf.org/html/rfc7396)")
    @PatchMapping(value = "/{id}")
    public Mono<ResponseEntity<Void>> patch(@PathVariable @NotNull final Long id,
                                            @RequestHeader(value = HttpHeaders.IF_MATCH) final Long version,
                                            @Valid @RequestBody final ItemPatchResource patch) {

        return itemService.findById(id, version, true)
                .map(item -> itemMapper.patch(patch, item))
                .flatMap(itemService::update)
                .map(itemId -> noContent().build());
    }

   ...

}