error

ipython nbconvert --to html --config cfg.py --template basic test.ipynb
[NbConvertApp] Using existing profile dir: u'/home/arymanus/.ipython/profile_default'
[NbConvertApp] Converting notebook test.ipynb to html
[NbConvertApp] Support files will be in test_files/
Traceback (most recent call last):
  File "/usr/local/bin/ipython", line 6, in <module>
    start_ipython()
  File "/usr/local/lib/python2.7/dist-packages/IPython/__init__.py", line 120, in start_ipython
    return launch_new_instance(argv=argv, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/IPython/config/application.py", line 564, in launch_instance
    app.start()
  File "/usr/local/lib/python2.7/dist-packages/IPython/terminal/ipapp.py", line 367, in start
    return self.subapp.start()
  File "/usr/local/lib/python2.7/dist-packages/IPython/nbconvert/nbconvertapp.py", line 268, in start
    self.convert_notebooks()
  File "/usr/local/lib/python2.7/dist-packages/IPython/nbconvert/nbconvertapp.py", line 301, in convert_notebooks
    output, resources = exporter.from_filename(notebook_filename, resources=resources)
  File "/usr/local/lib/python2.7/dist-packages/IPython/nbconvert/exporters/exporter.py", line 151, in from_filename
    return self.from_notebook_node(nbformat.read(f, 'json'), resources=resources, **kw)
  File "/usr/local/lib/python2.7/dist-packages/IPython/nbconvert/exporters/templateexporter.py", line 209, in from_notebook_node
    nb_copy, resources = super(TemplateExporter, self).from_notebook_node(nb, resources, **kw)
  File "/usr/local/lib/python2.7/dist-packages/IPython/nbconvert/exporters/exporter.py", line 123, in from_notebook_node
    nb_copy, resources = self._preprocess(nb_copy, resources)
  File "/usr/local/lib/python2.7/dist-packages/IPython/nbconvert/exporters/exporter.py", line 274, in _preprocess
    nbc, resc = preprocessor(nbc, resc)
  File "/usr/local/lib/python2.7/dist-packages/IPython/nbconvert/preprocessors/base.py", line 47, in __call__
    return self.preprocess(nb,resources)
  File "/usr/local/lib/python2.7/dist-packages/IPython/nbconvert/preprocessors/base.py", line 71, in preprocess
    worksheet.cells[index], resources = self.preprocess_cell(cell, resources, index)
  File "/usr/local/lib/python2.7/dist-packages/IPython/nbconvert/preprocessors/base.py", line 91, in preprocess_cell
    raise NotImplementedError('should be implemented by subclass')
NotImplementedError: should be implemented by subclass

If you suspect this is an IPython bug, please report it at:
    https://github.com/ipython/ipython/issues
or send an email to the mailing list at ipython-dev@scipy.org

You can print a more detailed traceback right now with "%tb", or use "%debug"
to interactively debug it.

Extra-detailed tracebacks for bug-reporting purposes can be enabled via:
    c.Application.verbose_crash=True