Sending Json along with multipart file in SpringBoot - json

Question

I'm trying to figure out how to pass a collection of optional parameters to a SpringBoot controller, along with a multipart file, but can't figure out how.
Without the multipart file, this works fine
public ResponseEntity<ViewModel> performOperationOnFilePath(#Valid #RequestBody final FileOperationFileContract requestBody)
where FileOperationFileContract is a POJO that looks like this
public class FileOperationFileContract {
#NotBlank(message = "The filepath is required")
private String filePath;
private Map<String, String> options = new HashMap<>();
#JsonAnyGetter
public Map<String, String> getOptions() {
return options;
}
#JsonAnySetter
public void setOptions(final String name, final String value) {
options.put(name, value);
}
}
Here's what I tried with the multipart file
public ResponseEntity<ViewModel> performOperationOnFile(#RequestParam(name="myfile") final MultipartFile file, #RequestPart(name="options", required=false) final FileOperationMultipartFileContract requestBody)
where FileOperationMultipartFileContract is a POJO that looks like this
public class FileOperationMultipartFileContract {
private Map<String, String> options = new HashMap<>();
#JsonAnyGetter
public Map<String, String> getOptions() {
return options;
}
#JsonAnySetter
public void setOptions(final String name, final String value) {
options.put(name, value);
}
}
This seems to work if I specify the Json payload in Postman like this (note that I must specify the content-type as application/json, or I get the message "'application/octet-stream' not supported"
But if there is no json part sent, I get a 403. I want the option collection to just be empty or null. In other words, I want it to default to {}
I've tried RequestPart and RequestParam, but there's no difference. I've also tried it with and without the #Valid annotation
How can I do this?
Update: I think that I figured out that my problem does not have as much to do with Spring as it does with what I'm trying to do with the #JsonAnyGetter and #JsonAnySetter annotations. If I change FileOperationFileContract to have regular fields, it works. But my guess is that the way I have it doesn't work very well with null. Although if the value is null, there should be no calls to setOptions. Any ideas?