ActionView::Template::Error (undefined method `safe_append=' for {:add_to_stack=>true}:Hash)

[vs37559]

ActionView::Template::Error (undefined method `safe_append=' for {:add_to_stack=>true}:Hash):
1: <% title = local_assigns[:title] || "PDF.js viewer" %>
2: <% pdf_url = local_assigns[:pdf_url] %>
3:
4:
5: <!--
6: Copyright 2012 Mozilla Foundation

pdfjs_viewer-rails (3f1549e) app/views/pdfjs_viewer/viewer/_viewer.html.erb:3

Rails: v6.1.3
Ruby: v3.0.1