title: No template sub-directory with name 'lab' found in the following paths
body: <p>I am running a python azure function which is running a jupyter notebook via the <code>nbconvert</code> API. This was working for a time, although without deploying new code I have started to get the following error:</p>
  <pre><code>No template sub-directory with name 'lab' found in the following paths:
      /home/.local/share/jupyter
      /usr/local/share/jupyter
      /usr/share/jupyter
  </code></pre>
  <p>The code I am using to achieve this is:</p>
  <pre><code>from nbconvert.preprocessors import ExecutePreprocessor
  from nbconvert import HTMLExporter
  
  ...
  
  dl = DictLoader({'footer':
  &quot;&quot;&quot;
  {%- extends 'full.tpl' -%}
  
  {% block input_group %}
      {%- if cell.metadata.get('nbconvert', {}).get('show_code', False) -%}
          ((( super() )))
      {%- endif -%}
  {% endblock input_group %}
  {% block output_group %}
      &lt;style&gt; .output_prompt{visibility:hidden;}&lt;/style&gt;
      {{ super() }}
  {% endblock output_group %}
  &quot;&quot;&quot;})
  
  ...
  
  html_exporter = HTMLExporter(extra_loaders=[dl], template_file='footer')
  html_exporter.template_name = 'classic'
  with open(JUPYTER_DIR + NOTEBOOK_NAME) as f:
      nb = nbformat.read(f, as_version=4)
  
  ep = ExecutePreprocessor(timeout=600, kernel_name='python')
  ep.preprocess(nb, {'metadata': {'path': JUPYTER_DIR}})
  (body, resources) = html_exporter.from_notebook_node(nb)
  </code></pre>
  <p>The functionapp is running the following:</p>
  <pre><code>python3.6
  nbconvert6.0.3
  jupyter-lab0.1.1
  </code></pre>
  <p>I have tried googling the error, the closest thing I have found so far is <a href="https://stackoverflow.com/questions/62431121/nbconvert-valueerror-no-template-sub-directory-with-name-rst-found-in-the-fo">this</a> which is similar but unanswered and not completely the same. Thought I'd post here to see if anyone knows how to resolve or for me to update if I manage to resolve the issue.</p>
  <p>I am quite confused as <code>lab</code> is not a keyword I am familiar with (outside of maybe <code>jupyterlab</code>) and isn't being used within the code.</p>
  <p>As for the paths mentioned:</p>
  <ul>
  <li><code>home/.local/share/jupyter/</code> exists and contains <code>nbconvert/templates/html</code></li>
  <li><code>usr/local/share/jupyter</code> &amp; <code>usr/share/jupyter</code> don't exist</li>
  </ul>
  <p>Thanks in advance for any help!</p>