Springboot MultipartFile response includes invalid json "inputStream" with no value

I am using Springboot to return a MultipartFile as my response for an endpoint.

        MultipartFile file = new MockMultipartFile(
            imageUploadResponse.getKey(), 
            imageUploadResponse.getKey(), 
            imageUploadResponse.getMimeType(), 
            imageUploadResponse.getInputStream()
        );
        return new ResponseEntity<>(file, headers, HttpStatus.OK);

However, the JSON returned to the client looks like this:

{ ..., "inputStream" }

Which is invalid JSON and breaks my $.ajax request. How do I fix this issue?

The issue was MockMultipartFile has a getter that does not serialize properly.

    @Override
    public InputStream getInputStream() throws IOException {
        return new ByteArrayInputStream(this.content);
    }

I solved it by extending MockMultipartFile

public class MultipartFileResponse extends MockMultipartFile {

  public MultipartFileResponse(String name, String originalFilename, String contentType, InputStream contentStream)
      throws IOException {
    super(name, originalFilename, contentType, contentStream);
  }

  // Parent class getInputStream is not serializable and
  // we don't need it, so we override and return null.
  @Override 
  public InputStream getInputStream() throws IOException {
    return null;
  }
  
}

Now inputStream is null in the JSON response, instead of a key with a missing value.