skip anotation if nil

lib/templates/build_annotations.rb

@@ -10,6 +10,7 @@ module Templates
       pdf.pages.flat_map.with_index do |page, index|
         annotations = page.objects.deref!(page.attributes[:Annots]) || []
         annotations.filter_map do |annot|
+          next if annot.nil?
           next if annot[:A].blank? || annot[:A][:URI].blank?
           next unless annot[:Subtype] == :Link
           next if !annot[:A][:URI].starts_with?('https://') && !annot[:A][:URI].starts_with?('http://')