Typescript Angular文件上传到Spring Boot失败，多部分边界拒绝

我正在try 将角形数据上传到Spring Boot服务器.

简单地说，在《春靴》中我接受:

data class Photo(
    val id: Long = 0L,
    val file: MultipartFile
)

data class PostRequest(
    @field:Size(min = 1, max = 100)
    val title: String,

    val photos: List<Photo> = mutableListOf()
)

通过控制器:

fun createPost(@Valid @ModelAttribute postRequest: PostRequest)

在Angular 上，我创建了这个形状:

this.postForm = this.fb.group({
   title: ["", [Validators.required, Validators.minLength(1)]],
   photos: this.fb.array([]),
});

当用户上传照片时，我将这些线路称为:

const photosArray = this.postForm.get("photos") as FormArray;
          
const newPhotoGroup = this.fb.group({
  id: "",
  file: event.target.result,
});
          
photosArray.push(newPhotoGroup);

最后，我构造了一个表单数据对象:

const formData = new FormData();
formData.append("title", this.postForm.get("title")?.value);
formData.append("photos", this.postForm.get("photos")?.value);

我使用此函数将此表单发布到API:

 postRequest<T>(url: string, body: any): Observable<HttpResponse<T>> {
    const headers = new HttpHeaders({
      "Content-Type": "multipart/form-data",
    });

    return this.http.post<T>(url, body, {
      headers,
      observe: "response",
      withCredentials: true,
    });
  }

在开发人员工具中，我看到以下请求:

Spring Boot抱怨道:

org.apache.tomcat.util.http.fileupload.FileUploadException: the request was rejected because no multipart boundary was found

谁来给我开导一下.谢谢.