Cannot read property 'source' of undefined

[roblourens]

When I run the RBL tests, I see this error

rejected promise not handled within 1 second: TypeError: Cannot read property 'source' of undefined
/Applications/Visual Studio Code - Insiders.app/Contents/Resources/app/out/bootstrap-fork.js:5
stack trace: TypeError: Cannot read property 'source' of undefined
    at callScopes (/Users/roblou/code/vscode-jupyter/src/client/datascience/jupyter/debuggerVariables.ts:253:32)
/Applications/Visual Studio Code - Insiders.app/Contents/Resources/app/out/bootstrap-fork.js:5

The DebuggerVariables code is throwing for a stackTrace response that has an empty stackFrames array

{"seq":27,"type":"response","request_seq":20,"success":true,"command":"stackTrace","body":{"stackFrames":[],"totalFrames":1}}