minio uploads files as folders using aws sdk

I upload files to minio, using such code

  s3AsyncClient.putObject(
        PutObjectRequest.builder()
            .bucket(minioConfigurationProperties.bucket)
            .contentType(URLConnection.guessContentTypeFromStream(inputStream))
            .contentLength(size)
            .key(destinationPath)
            .build(),
        AsyncRequestBody.fromBytes(inputStream.readAllBytes())
    ).join()

but my files look like filders:

for example: if i upload example.json then i see in web ui folder with name example.json/ with zero size. What does it mean? what am i doing worng?