COSArray.getObject() incorrect handling of indirect reference to COSNull

java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.io.IOException: Error: Unknown annotation type COSNull{}
    org.apache.pdfbox.debugger.pagepane.PagePane$RenderWorker.done(PagePane.java:175)
    sun.swing.AccumulativeRunnable.run(Unknown Source)
    java.security.AccessController.doPrivileged(Native Method)
    java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
Caused by: java.util.concurrent.ExecutionException: java.io.IOException: Error: Unknown annotation type COSNull{}
    org.apache.pdfbox.debugger.pagepane.PagePane$RenderWorker.done(PagePane.java:164)
    sun.swing.AccumulativeRunnable.run(Unknown Source)
    java.security.AccessController.doPrivileged(Native Method)
    java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
Caused by: java.io.IOException: Error: Unknown annotation type COSNull{}
    org.apache.pdfbox.pdmodel.interactive.annotation.PDAnnotation.createAnnotation(PDAnnotation.java:164)
    org.apache.pdfbox.pdmodel.PDPage.getAnnotations(PDPage.java:664)
    org.apache.pdfbox.rendering.PageDrawer.drawPage(PageDrawer.java:181)
    org.apache.pdfbox.rendering.PDFRenderer.renderPage(PDFRenderer.java:208)
    org.apache.pdfbox.rendering.PDFRenderer.renderImage(PDFRenderer.java:139)
    org.apache.pdfbox.rendering.PDFRenderer.renderImage(PDFRenderer.java:68)
    org.apache.pdfbox.debugger.pagepane.PagePane$RenderWorker.doInBackground(PagePane.java:155)
    org.apache.pdfbox.debugger.pagepane.PagePane$RenderWorker.doInBackground(PagePane.java:138)
    java.lang.Thread.run(Unknown Source)

    public COSBase getObject( int index )
    {
        Object obj = objects.get( index );
        if( obj instanceof COSObject )
        {
            obj = ((COSObject)obj).getObject();
        }
        else if( obj instanceof COSNull )
        {
            obj = null;
        }
        return (COSBase)obj;
    }