why ? Jupyter --500 : Internal Server Error

Last login: Tue Oct  9 04:01:40 on ttys000
appledeMacBook-Pro:~ apple$ jupyter notebook
[I 05:44:15.864 NotebookApp] [jupyter_nbextensions_configurator] enabled 0.4.0
[I 05:44:15.864 NotebookApp] Serving notebooks from local directory: /Users/apple
[I 05:44:15.864 NotebookApp] The Jupyter Notebook is running at:
[I 05:44:15.864 NotebookApp] http://localhost:8888/?token=4786096d5947b3bcda5eadf5e64cc0a9ee2f4f7070e1c4fc
[I 05:44:15.864 NotebookApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
[C 05:44:15.866 NotebookApp]

    Copy/paste this URL into your browser when you connect for the first time,
    to login with a token:
        http://localhost:8888/?token=4786096d5947b3bcda5eadf5e64cc0a9ee2f4f7070e1c4fc
[I 05:44:16.262 NotebookApp] Accepting one-time-token-authenticated connection from ::1
[E 05:44:23.127 NotebookApp] Uncaught exception GET /notebooks/Markdown%E8%AF%AD%E6%B3%95.ipynb (::1)
    HTTPServerRequest(protocol='http', host='localhost:8888', method='GET', uri='/notebooks/Markdown%E8%AF%AD%E6%B3%95.ipynb', version='HTTP/1.1', remote_ip='::1')
    Traceback (most recent call last):
      File "/usr/local/lib/python3.7/site-packages/tornado/web.py", line 1590, in _execute
        result = method(*self.path_args, **self.path_kwargs)
      File "/usr/local/lib/python3.7/site-packages/tornado/web.py", line 3006, in wrapper
        return method(self, *args, **kwargs)
      File "/usr/local/lib/python3.7/site-packages/notebook/notebook/handlers.py", line 59, in get
        get_custom_frontend_exporters=get_custom_frontend_exporters
      File "/usr/local/lib/python3.7/site-packages/notebook/base/handlers.py", line 467, in render_template
        return template.render(**ns)
      File "/usr/local/lib/python3.7/site-packages/jinja2/asyncsupport.py", line 76, in render
        return original_render(self, *args, **kwargs)
      File "/usr/local/lib/python3.7/site-packages/jinja2/environment.py", line 1008, in render
        return self.environment.handle_exception(exc_info, True)
      File "/usr/local/lib/python3.7/site-packages/jinja2/environment.py", line 780, in handle_exception
        reraise(exc_type, exc_value, tb)
      File "/usr/local/lib/python3.7/site-packages/jinja2/_compat.py", line 37, in reraise
        raise value.with_traceback(tb)
      File "/usr/local/lib/python3.7/site-packages/notebook/templates/notebook.html", line 1, in top-level template code
        {% extends "page.html" %}
      File "/usr/local/lib/python3.7/site-packages/notebook/templates/page.html", line 154, in top-level template code
        {% block header %}
      File "/usr/local/lib/python3.7/site-packages/notebook/templates/notebook.html", line 120, in block "header"
        {% for exporter in get_custom_frontend_exporters() %}
      File "/usr/local/lib/python3.7/site-packages/notebook/notebook/handlers.py", line 24, in get_custom_frontend_exporters
        exporter = get_exporter(name)()
      File "/usr/local/lib/python3.7/site-packages/jupyter_contrib_nbextensions/nbconvert_support/collapsible_headings.py", line 44, in __init__
        collapsible_headings_options = cm.get('notebook').get(
      File "/usr/local/lib/python3.7/site-packages/notebook/services/config/manager.py", line 25, in get
        recursive_update(config, cm.get(section_name))
      File "/usr/local/lib/python3.7/site-packages/notebook/config_manager.py", line 103, in get
        recursive_update(data, json.load(f))
      File "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__init__.py", line 296, in load
        parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)
      File "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__init__.py", line 348, in loads
        return _default_decoder.decode(s)
      File "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/decoder.py", line 337, in decode
        obj, end = self.raw_decode(s, idx=_w(s, 0).end())
      File "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/decoder.py", line 353, in raw_decode
        obj, end = self.scan_once(s, idx)
    json.decoder.JSONDecodeError: Expecting ',' delimiter: line 19 column 5 (char 550)
[E 05:44:23.137 NotebookApp] {
      "Host": "localhost:8888",
      "Cookie": "username-localhost-8888=\"2|1:0|10:1539035056|23:username-localhost-8888|44:YTYyN2VhMDY2YmJmNDM5YTg5YmY3YzYwZjMxMzg0ZTg=|8259c37ffc70f13cb31c48b734cd0036cec9bf194d0a93640d9b6b4afe8b2367\"; username-localhost-8890=\"2|1:0|10:1538453361|23:username-localhost-8890|44:ZTM5MDlmOGMyMTNkNGE5NGIwZTU1ZGU5Y2ViMGI5MzE=|2451aa80ce36fcf1e1c3357777905260bcffa592429a6efcf8ee7e645eafbf1b\"; username-localhost-8889=\"2|1:0|10:1538452536|23:username-localhost-8889|44:ZDc0ZDI0ZTU2OTY0NDgxN2JkY2UwZTNjZmVkNDQ2OGM=|6314bf92f8e2a6c8a6b9d134e211882b6f325c5731b9ef4e2d0a2350a785302f\"; _xsrf=2|353bcb8e|3506e6253847e9da558f83df41979688|1536852952",
      "Connection": "keep-alive",
      "Upgrade-Insecure-Requests": "1",
      "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
      "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.0 Safari/605.1.15",
      "Referer": "http://localhost:8888/tree",
      "Accept-Language": "zh-cn",
      "Accept-Encoding": "gzip, deflate"
    }
[E 05:44:23.137 NotebookApp] 500 GET /notebooks/Markdown%E8%AF%AD%E6%B3%95.ipynb (::1) 202.41ms referer=http://localhost:8888/tree

The traceback names notebook/notebook/handlers.py, notebook/base/handlers.py, notebook/config_manager.py, and jupyter_contrib_nbextensions/nbconvert_support/collapsible_headings.py; start by inspecting the JSON loaded while opening Markdown语法.ipynb. Reproduce the 500 response and establish done as opening the notebook without this server error, with a regression test if the repository supports one.