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Radio button group across distant pages causes null-reference error and breaks page rendering

Summary

When a PDF contains radio button fields with the same name (same group) on different, distant pages, scrolling between those pages causes a runtime error in FormDesigner2.renderFormFieldsInZooming. On heavier PDFs this can completely block further page rendering and leave the viewer in a permanent loading state.

This problem reproduces only with radio buttons. Other form field types with the same name across pages (e.g. text inputs, checkboxes) do not trigger this error.

Steps to reproduce

  1. Open the online demo: Stackblitz. The demo uses Syncfusion Standalone PDF Viewer in an Angular application and loads a sample PDF [assets/rendering-issue.pdf] with 25 pages.
  2. 
    Open the browser DevTools console
  3. Wait until the application and the PDF document are fully loaded.
  4. Scroll to page 9. On this page there are two radio button fields that share the same name (group): rbtn.
  5. Scroll to page 24. On this page there are two more radio button fields with the same name rbtn. These radio buttons belong to the same group as the fields on page 9.
  6. Scroll back up to page 9.
  7. As soon as page 9 starts rendering again, the following error appears in the console:

  8. TypeError: Cannot read properties of null (reading 'appendChild') at FormDesigner2.renderFormFieldsInZooming
  9. On heavier or more complex PDFs, after this error appears, some pages stop rendering and the viewer may show an infinite loader and never finish rendering the remaining pages.
Expected behavior
Scrolling between pages that contain radio button fields with the same group name across multiple pages should not throw any errors. All pages should render correctly when scrolled into view, even if radio buttons belong to the same group and are located on different pages. The viewer should not get stuck in a permanent loading state because of form field rendering.

Actual behavior

After visiting a later page (page 24) that has radio buttons in the same group name (rbtn) as radio buttons on an earlier page (page 9), then scrolling back to the earlier page triggers a runtime error:

TypeError: Cannot read properties of null (reading 'appendChild')
    at FormDesigner2.renderFormFieldsInZooming


On more complex/heavy PDFs, this error sometimes prevents further pages from rendering at all, and the viewer shows an endless loading indicator.