title: PDFBox child cannot be cast as a PDField in version 1.8.9
body: <p>I am using PDFBox to populate fields in PDF Files.  I am currently using version 1.6.0 and the code works.  I tried to update to version 1.8.9 and the child elements are not being seen as a PDField.  The "kid instanceof PDField" always returns false and if I try to cast it as a PDField I get "Cannot cast 'org.apache.pdfbox.pdmodel.interactive.annotation.PDAnnotationWidget' to 'org.apache.pdfbox.pdmodel.interactive.form.PDField'".  The code works fine on the older version.  Do I need to handle this differently in the newer version of PDFBox?  Fields that do not have children elements work fine.  In this case the same field is displayed in 2 locations on the PDF.  </p>
  
  <pre><code>List&lt;COSObjectable&gt; kids = field.getKids();
      if (kids != null) {
          if (!parent.equals(field.getPartialName())) {
              parent = parent + "." + field.getPartialName();
          }
          for (COSObjectable kid : kids) {
              if (kid instanceof PDField) {
                  processField(result, pages, (PDField) kid, parent);
              }
          }
  </code></pre>