$ jupyter nbextension enable jupyter_notebook_gist --user --py
Enabling notebook extension jupyter-notebook-gist/extension...
Traceback (most recent call last):
  File "/Users/rpa/anaconda/bin/jupyter-nbextension", line 6, in <module>
    sys.exit(notebook.nbextensions.main())
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/jupyter_core/application.py", line 267, in launch_instance
    return super(JupyterApp, cls).launch_instance(argv=argv, **kwargs)
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/traitlets/config/application.py", line 596, in launch_instance
    app.start()
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/notebook/nbextensions.py", line 969, in start
    super(NBExtensionApp, self).start()
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/jupyter_core/application.py", line 256, in start
    self.subapp.start()
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/notebook/nbextensions.py", line 877, in start
    self.toggle_nbextension_python(self.extra_args[0])
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/notebook/nbextensions.py", line 853, in toggle_nbextension_python
    logger=self.log)
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/notebook/nbextensions.py", line 459, in enable_nbextension_python
    logger=logger)
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/notebook/nbextensions.py", line 380, in _set_nbextension_state_python
    for nbext in nbexts]
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/notebook/nbextensions.py", line 345, in _set_nbextension_state
    cm.update(section, {"load_extensions": {require: state}})
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/traitlets/config/manager.py", line 85, in update
    data = self.get(section_name)
  File "/Users/rpa/anaconda/lib/python2.7/site-packages/traitlets/config/manager.py", line 63, in get
    return json.load(f)
  File "/Users/rpa/anaconda/lib/python2.7/json/__init__.py", line 291, in load
    **kw)
  File "/Users/rpa/anaconda/lib/python2.7/json/__init__.py", line 339, in loads
    return _default_decoder.decode(s)
  File "/Users/rpa/anaconda/lib/python2.7/json/decoder.py", line 364, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/Users/rpa/anaconda/lib/python2.7/json/decoder.py", line 382, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded

$ jupyter --version
4.1.0
$ jupyter notebook --version
4.3.0