Debugging Typescript in VS Code - doesn't work when using an import

I have a simple file to debug, index.ts.

It will debug fine until I add this line to the top of the code page:

import * as doten开发者_Go百科v from 'dotenv';

Then I can see it starts to go into debug mode and then exits wihtout hitting a breakpoint.

Is there a work-around for this?