Pass document to universal_viewer for index view.

app/helpers/application_helper.rb

@@ -52,7 +52,7 @@ def readonly?(field)
   # @param image_options [Hash]
   # @return [Array<String>] an Array containing the URLs to the thumbnails
   def document_thumbnail(document, image_options = {})
-    return unless !current_exhibit.nil? && current_exhibit.thumbnails_enabled && !universal_viewer.nil?
+    return unless !current_exhibit.nil? && current_exhibit.thumbnails_enabled && !universal_viewer(document).nil?
 
     values = document.fetch(:thumbnail_ssim, nil)
     return if values.empty?
@@ -78,12 +78,12 @@ def universal_viewer_installation_url
 
     # Construct the object used to handle Universal Viewer installations
     # @return [UniversalViewer]
-    def universal_viewer
-      return if @document.nil?
+    def universal_viewer(document = @document)
+      return if document.nil?
 
       UniversalViewer.new(
         universal_viewer_installation_url,
-        manifest: @document.manifest,
+        manifest: document.manifest,
         config: universal_viewer_config_url
       )
     end