Jupyter notebook failed to launch. TypeError: Cannot read property 'toLocaleLowerCase' of undefined

Environment data

• VS Code version: 1.29.1
• Extension version (available under the Extensions sidebar): Python extension 2018.11.0
• OS and version: Windows 10
• Python version (& distribution if applicable, e.g. Anaconda): Python 3.6 (on path)
• Type of virtual environment used (N/A | venv | virtualenv | conda | …): N/A
• Relevant/affected Python packages and their versions: jupyter notebook server 5.7.2

Expected behaviour

Run notebook cell:

#%%
import requests

Actual behaviour

N/A

Logs

Output from Console under the Developer Tools panel (toggle Developer Tools on under Help)

workbench.main.js:sourcemap:2429 Jupyter notebook failed to launch.  TypeError: Cannot read property 'toLocaleLowerCase' of undefined

workbench.main.js:sourcemap:294 [Extension Host] Failed to get interpreter information for 'C:\Program Files\nodejs\node.exe' SyntaxError: Unexpected token C in JSON at position 0
	at JSON.parse (<anonymous>)
	at d.<anonymous> (C:\Users\klo\.vscode\extensions\ms-python.python-2018.11.0\out\client\extension.js:83:285742)
	at Generator.next (<anonymous>)
	at s (C:\Users\klo\.vscode\extensions\ms-python.python-2018.11.0\out\client\extension.js:83:284981)
	at <anonymous>

workbench.main.js:sourcemap:294 [Extension Host] Python Extension: Error: Jupyter notebook failed to launch. 
TypeError: Cannot read property 'toLocaleLowerCase' of undefined

[rchiodo]

This should be fixed in our insiders build

[rchiodo]

You can enumerate your kernelspecs with ‘jupyter kernelspec list’.

One of the kernelspecs listed is missing the language or path in the json.

We recently started forcing a kernel spec so that’s the likely cause. Our code is not checking that the language element is missing, and hence the crash.