文件上传：意外令牌 JSON 中的位置 0

Question

我已将文件上传到服务器，但始终返回此错误：

SyntaxError: Unexpected token � in JSON at position 0
    at JSON.parse (<anonymous>)
    at createStrictSyntaxError (/home/andre/projetos/rifa/parse-server/node_modules/body-parser/lib/types/json.js:158:10)
    at parse (/home/andre/projetos/rifa/parse-server/node_modules/body-parser/lib/types/json.js:83:15)
    at /home/andre/projetos/rifa/parse-server/node_modules/body-parser/lib/read.js:121:18
    at invokeCallback (/home/andre/projetos/rifa/parse-server/node_modules/raw-body/index.js:224:16)
    at done (/home/andre/projetos/rifa/parse-server/node_modules/raw-body/index.js:213:7)
    at IncomingMessage.onEnd (/home/andre/projetos/rifa/parse-server/node_modules/raw-body/index.js:273:7)
    at IncomingMessage.emit (events.js:387:35)
    at endReadableNT (internal/streams/readable.js:1317:12)
    at processTicksAndRejections (internal/process/task_queues.js:82:21)

我要发送的客户端代码在 Flutter 中：

Future<void> alterarImagemRifa() async {
    var img = await ImagePicker().getImage(source: ImageSource.gallery);
    ParseFileBase parseFile;
    if (kIsWeb) {
      ParseWebFile file = ParseWebFile(null, name: null, url: img.path);
      await file.download();
      parseFile = ParseWebFile(file.file, name: 'imagens/rifa_${rifa.id}');
      // parseFile = ParseWebFile(await img.readAsBytes(), name: 'imagens/rifa_${rifa.id}', debug: true);
    } else {
      parseFile = ParseFile(File(img.path), name: 'imagens/rifa_${rifa.id}');
    }

    obj.set('imagem', parseFile );
    var resp = await obj.save().catchError(erroSnack);
    if(!resp.success)
      return erroSnack('Não foi possível enviar o arquivo ao servidor', StackTrace.current);
    rifa.imagem = parseFile.url;
  }

我没有解析平台的经验，任何帮助都会非常好