Spring MockBean is null

I want to test the PostMapping of my controller. It should receive a multipartfile and 2 boolean parameters, and return a response as an InputStreamRessource (I used this as it is easy with Spring). Therefore, I want to mock the beans (services). However, it seems that even though the service is correctly called, the output is always null.

Here is my controller:

    @PostMapping(value = "/file",
        consumes = MediaType.MULTIPART_FORM_DATA_VALUE,
        produces = MediaType.TEXT_HTML_VALUE)
public ResponseEntity<InputStreamResource> parseMultipartFile(
        @RequestParam MultipartFile multipartFile,
        @RequestParam boolean hasOnlyOneSheet,
        @RequestParam boolean hasBorders) throws IOException {

    String fileContentType = multipartFile.getContentType();
    if (mimeType.contains(fileContentType)) {

        // Call service
        InputStream parsedFile = multipartFileToHtmlService.multipartFileToHtml(multipartFile, hasOnlyOneSheet, hasBorders);
        
        // Convert the result as InputStreamRessource to return
        InputStreamResource inputStreamResource = new InputStreamResource(parsedFile);

        return ResponseEntity.ok(inputStreamResource);
    } else {
        throw new UnsupportedImportMediaTypeException("Wrong file type;\n Import .xls or .xlsx file");
    }
}

And the corresponding test Class:

@WebMvcTest
@RunWith(SpringRunner.class)
class HtmlExporterControllerTest {

@MockBean
MultipartFileToHtmlService multipartFileToHtmlService;

@MockBean
BeanFactory beanFactory;

@Autowired
MockMvc mockMvc;

@Test
public void parseMultipartFile_Should_Return_Ok() throws Exception {
    MockMultipartFile mockMultipartFile = new MockMultipartFile(
            "multipartFile",
            "test.xls",
            "application/xls",
            "Hello World!".getBytes());


mockMvc.perform(multipart("/file").file(mockMultipartFile)
            .param("hasOnlyOneSheet", "true")
            .param("hasBorders", "true"))
            .andExpect(status().isOk())
            .andReturn();
    }
}

For better explanation, here is a screenshot of my debug session while running the test:

As you can see, parsedFile is always null, I don't know why.

I also want to precise that it is working during manual testing, I do get the expected output, I just can't find a way to UnitTest my controller.