Ошибка декодирования JSON: неверный стартовый байт UTF-8 0xb0

Question

У меня проблема, когда я запускаю Junit для этого метода:

          public ResponseEntity<InputStreamResource> xlsexp(@RequestHeader MultiValueMap<String, String> headerMap,
            @RequestBody ExRequest request) {
        HttpHeaders headers = new HttpHeaders();
        headers.add("Content-Disposition", "attachment; filename=example.xls");
        
        return ResponseEntity
                .ok()
                .headers(headers)
                .body(exportatorService.exportToXls(request));
    }

И тест такой:

          public void testing_01() {
        this.webClient.post()
            .uri("/xlsexp")
            .accept(MediaType.APPLICATION_JSON_UTF8)
            .header(...., ....)
            .
            .
            .body(BodyInserters.fromValue(request))
            .exchange()
            .expectStatus().isEqualTo(HttpStatus.OK)
            .expectBody(ResponseEntity.class);
    }

И исключение:

      org.springframework.core.codec.DecodingException: JSON decoding error: Invalid UTF-8 start byte 0xb0; nested exception is com.fasterxml.jackson.core.JsonParseException: Invalid UTF-8 start byte 0xb0
 at [Source: (org.springframework.core.io.buffer.DefaultDataBuffer$DefaultDataBufferInputStream); line: 1, column: 12]
    at org.springframework.http.codec.json.AbstractJackson2Decoder.processException(AbstractJackson2Decoder.java:242)
    Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
    |_ checkpoint ⇢ Body from POST /xlsexp [DefaultClientResponse]
Stack trace:
        at org.springframework.http.codec.json.AbstractJackson2Decoder.processException(AbstractJackson2Decoder.java:242)
        at org.springframework.http.codec.json.AbstractJackson2Decoder.decode(AbstractJackson2Decoder.java:198)
        at org.springframework.http.codec.json.AbstractJackson2Decoder.lambda$decodeToMono$1(AbstractJackson2Decoder.java:179)
        at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:125)
        at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107)
        at reactor.core.publisher.FluxMapFuseable$MapFuseableConditionalSubscriber.onNext(FluxMapFuseable.java:295)
        at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.onNext(FluxFilterFuseable.java:337)

Я намерен протестировать с помощью Junit метод экспорта в Excel. Вы хоть представляете, что может происходить?

Спасибо