MockMultipartFile created from text file is not read properly in Spring Boot

Given this two tests:

@Test
    public void testFileUpload1() throws Exception {
        byte[] fileContent = "bar".getBytes(Charset.forName("UTF-8"));
        MockMultipartFile file = new MockMultipartFile("file", "orig", null, fileContent);

        mockMvc.perform(fileUpload("/upload")
                .file(file))
                .andExpect(status().isCreated());
}

and

@Test
    public void testFileUpload2() throws Exception {
        final Path path = Paths.get(getClass().getClassLoader().getResource("text_file.csv").getPath());
        final byte[] fileContent  = java.nio.file.Files.readAllBytes(path);
        MockMultipartFile file = new MockMultipartFile("file", "orig", null, fileContent);

        mockMvc.perform(fileUpload("/upload")
                .file(file))
                .andExpect(status().isCreated());
}

Then the first test passes, the second fails with message

org.springframework.web.bind.MissingServletRequestParameterException: Required MultipartFile parameter 'file' is not present

What's wrong with the mocked MultipartFile constructed via the real File?

Observe that I can read the csv file, e.g. with:

try {
            try (BufferedReader br = new BufferedReader(new FileReader(new File(getClass().getClassLoader().getResource("text_file.csv").getFile())))) {
                String line;
                while ((line = br.readLine()) != null) {
                    System.out.println(line);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }