Nativescript - Can't upload image to server

Question

I can't upload an image to external server from my app. When I try do this, VSCode return: ERROR Error: Cannot convert object to Ljava/lang/String; at index 0 . I use nativescript-background-http plugin in my app. My code:

    private file: string;
    private url: string;
    private counter: number = 0;
    private session: any;
    public events: { eventTitle: string, eventData: any }[] = [];
    constructor(private gallery: GalleryService, private params: ModalDialogParams) {
        this.image = params.context;
        var pict = new Image();
        pict.src = this.image;
        console.log(pict.src);
        this.file = pict.src;
        this.url = "http://127.0.0.1:80";
        this.session = bgHttp.session("image-upload");
    }
    uploadPhoto() {
        const name = this.file;
        const description = "Upload";
        const request = {
            url: this.url,
            method: "POST",
            headers: {
                "Content-Type": "application/octet-stream",
                "File-Name": name
            },
            description: description,
            androidAutoDeleteAfterUpload: false,
            androidNotificationTitle: 'NS HTTP back',
        };
        let task: bgHttp.Task;
        task = this.session.uploadFile(this.file, request);
    }