The issue is in how you're handling file uploads in your frontend code. The MultipartException occurs because:

1- You're adding enctype="multipart/form-data" to your form, but the form isn't actually being submitted, instead you're using Axios directly.

2- Your Axios request in addNewAsset() isn't configured to send multipart/form-data:

addNewAsset(asset) {
    return axios.post(ASSETS_GOT_FROM_REST_API, asset);
}

3- Your Spring controller expects @RequestParam files but is receiving them as part of the @RequestBody

this is all the problem i saw.

also use FormData in your JavaScript to properly handle multipart uploads.