Angular - downloaded File from Backend contains only [object Object]

Question

I am trying to download a DMN File, which is basically a XML File, which I get from Spring Boot Backend. I am sure that the backend works, because the HTTP Request is succesful and I get some byte Array as response from backend, and also if I try with Postman, I get the right file and content.

But if try to open the file in my Angular App, the file just contains [object Object] as content.

Here is my code:

Backend:

@GetMapping(path = "/dmn-definition/{dmnId}/download")
public ResponseEntity<byte[]> downloadDMNById(@ApiParam(required = true) @PathVariable String dmnId) {
    String xml = IoUtil.inputStreamAsString(repositoryService
            .getDecisionModel(dmnId));

    HttpHeaders headers = new HttpHeaders();
    headers.setCacheControl("must-revalidate, post-check=0, pre-check=0");
    headers.add(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + dmnId + ".dmn");

    byte[] content = xml.getBytes();

    return ResponseEntity.ok()
            .headers(headers)
            .contentLength(content.length)
            .contentType(MediaType.APPLICATION_OCTET_STREAM)
            .body(content);
}

Frontend:

downloadDmnFileById(id: string): Observable<ArrayBuffer> {
const httpOptions : Object = {
  headers: new HttpHeaders({
    'Accept': 'application/octet-stream',
  }),
  responseType: 'blob',
  observe: 'response'
};
return this.httpClient.get<ArrayBuffer>(`${baseUrl}/dmn-definition/${id}/download`, httpOptions);

}

onDownloadDmnFile(dmn: Dmn): void { 
this.dmnService
    .downloadDmnFileById(dmn.id, this.processGroupName)
    .subscribe((result) => {
      const a = document.createElement('a');
      document.body.appendChild(a);
      let binaryData = [];
      binaryData.push(result);
      const blob = new Blob(binaryData, { type: 'application/xml' });
      const url = window.URL.createObjectURL(blob);
      a.href = url;
      a.download = dmn.id + ".dmn";
      a.click();
      window.URL.revokeObjectURL(url);
    });
}