File input dont upload when set attr

[dominhnhien1997]

I have a class for Form
public class UploadFileForm { [FileUploadEditor] public string MyFile { get; set; } }
I used that class for a dialog like this:
`export class UploadFileDialog extends PropertyDialog<any, UploadFileDialogOptions> {

protected getFormKey() { return UploadFileForm.formKey; }
protected form: UploadFileForm;
public onAfterUploadingCallback: (fileName: string) => void;

constructor(opt?: WidgetProps<UploadFileDialogOptions>) {
    super(opt);
    this.form = new UploadFileForm(this.idPrefix);
    this.dialogTitle = "Upload File";

    Fluent(this.domNode).findFirst<HTMLInputElement>('input[type="file"]').attr('accept', '.pdf');

    this.form.MyFile.element.closest(".field").findAll(".caption").forEach(x => Fluent(x).remove());

}

}}
`
but when I set attr for input, the file upload action was not performed. If I comment the line
Fluent(this.domNode).findFirst('input[type="file"]').attr('accept', '.pdf');
everything works as expected

I really don't understand what is causing this problem. Please help me.
Version serenity : 8.4.8