ts-loader: 'externals' in webpack.config.js is ignored

With a webpack config file that has an externals section eg:

module.exports = {
    ...
    externals: {
        hello: true
    },
    ...
}

This section isn’t used by ts-loader and the compile will fail because the module hello can’t be found.

The same project compiles fine from javascript files without ts-loader.

Sample project at https://github.com/stkb/ts-loader-issue