Jupyter 500 : Internal Server Error – cannot import name ConverterMapping

ImportError: cannot import name ConverterMapping
[E 16:24:24.485 NotebookApp] {
      "Accept-Language": "en-US,en;q=0.5", 
      "Accept-Encoding": "gzip, deflate", 
      "Host": "localhost:8888", 
      "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8", 
      "User-Agent": "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:70.0) Gecko/20100101 Firefox/70.0", 
      "Connection": "keep-alive", 
      "Referer": "http://localhost:8888/tree", 
      "Cookie": "username-localhost-8888=\"2|1:0|10:1574810660|23:
username-localhost-8888|44:ODYwMDdiMDE4MGRjNDkwOWFiMjBlZmI1MThiODY3OTg=|
840976561750da22820e615382453a3a38d20a7e359f75871c3623b1e4d9ebfe\"; 
_xsrf=2|fe88647d|9b98777c28dce1ff0e17b5f3038d75f6|1574805739", 
      "Upgrade-Insecure-Requests": "1"
    }
[E 16:24:24.485 NotebookApp] 500 GET /notebooks/PytorchTensors.ipynb (127.0.0.1) 189.22ms referer=http://localhost:8888/tree

And this was what worked for me to fix the problem.

conda install --channel=conda-forge nb_conda_kernels