PDAnnotationLink::getBorderStyle() don't understand external border style

getBorderStyle() trying to get "BS" property and convert it to COSDictionary:

 COSDictionary bs = (COSDictionary) this.getDictionary().getItem(
                COSName.getPDFName( "BS" ) );

But it doesn't work when style is in external object and linked by reference (see example attached in project zip):

Exception in thread "main" java.lang.ClassCastException: org.apache.pdfbox.cos.COSObject cannot be cast to org.apache.pdfbox.cos.COSDictionary
at org.apache.pdfbox.pdmodel.interactive.annotation.PDAnnotationLink.getBorderStyle(PDAnnotationLink.java:131)
at org.accusoft.example.Bug.main(Bug.java:17)

I think it need something like conditional second getDictionary() here.