Fix empty leaf pages after hugo update

themes/book/layouts/partials/docs/menu-filetree.html

 <!-- Put configured sections list to .Scratch -->
-{{ template "book-get-root-section" . }} 
+{{ template "book-get-root-section" . }}
 
 {{- range .Scratch.Get "BookSections" -}}
   {{ template "book-section" (dict "Section" . "CurrentPage" $.Permalink) }}
     {{ end }}
 
     {{ range .Section.Pages }}
-    <li>
-      {{ template "book-page-link" (dict "Page" . "CurrentPage" $.CurrentPage) }}
-    </li>
+      {{- if .Content -}}
+        <li>
+          {{ template "book-page-link" (dict "Page" . "CurrentPage" $.CurrentPage) }}
+        </li>
+     {{- end -}}
     {{ end }}
   </ul>
 {{ end }}
     {{ $bookSections := where .Site.Sections "Section" $bookSection }}
     {{ .Scratch.Set "BookSections" $bookSections }}
   {{ end }}
-{{ end }}
+{{ end }}