Restore None check condition in HTML exporter instead of _init_resources

Fix index.html.j2 to restore the style of the table of content.

nbconvert/exporters/html.py

@@ -266,8 +266,8 @@ def from_notebook_node(  # type:ignore[explicit-override, override]
                 markdown_collection = markdown_collection + cell.source + "\n"
 
         resources = self._init_resources(resources)
-        print('type:', resources)
-
+        if resources is None:
+            resources = {}
         resources["tableofcontents"] = extract_titles_from_markdown_input(markdown_collection)
 
         filter_data_type = WidgetsDataTypeFilter(
@@ -356,8 +356,7 @@ def resources_include_url(name):
             return markupsafe.Markup(src)
 
         resources = super()._init_resources(resources)
-
-
+
         resources["theme"] = self.theme
         resources["include_css"] = resources_include_css
         resources["include_lab_theme"] = resources_include_lab_theme

share/templates/lab/index.html.j2

@@ -181,24 +181,25 @@ a.anchor-link {
 <div class="jp-RenderedHTMLTOC-Title">Table of contents</div>
 {%- for item in resources.tableofcontents -%}
 {%- set (level, text, id, href) = item -%}
-<div
+<div class="
 {%- if level==1 -%}
-class="jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h1"
+jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h1
 {%- elif level==2 -%}
-class="jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h2"
+jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h2
 {%- elif level==3 -%}
-class="jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h3"
+jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h3
 {%- elif level==4 -%}
-class="jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h4"
+jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h4
 {%- elif level==5 -%}
-class="jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h5"
+jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h5
 {%- elif level==6 -%}
-class="jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h6"
-{%- endif -%}
-></div>
+jp-RenderedHTMLCommon jp-RenderedHTMLTOC-Item-h6
+{%- endif -%}"
+>
 <a href={{href}}>
 {{text}}
 </a>
+</div>
 {%- endfor -%}
 {%- endif -%}
 {% endblock tableofcontents %}