Comm documentation examples result in error

I am trying to follow the documentation for setting up a Comm as described here:
http://jupyter-notebook.readthedocs.io/en/latest/comms.html

However, there appears to be _something_ missing as if I try to insert the
code from the "opening a Comm from the kernel" into my kernel.py,
I end up getting the following error:

AttributeError: 'NoneType' object has no attribute 'session'

The error is triggered when executing:

c.send(...)

If I instead insert the code from the "opening a comm from the frontend",
I get the following error:

get_ipython is not defined

Start with the Comm documentation at the linked comms.html page and reproduce both examples in their stated kernel and frontend contexts. Check the reported NoneType session and undefined get_ipython errors, then update the examples or their instructions so both run without those errors and verify the revised documentation.

Written by the indexing model from the issue text.