Can't use with babel-plugin-transform-es2015-modules-systemjs

[aaronmars]

Is this intended to be used with the main Systemjs module transform?
If so, I am getting an error just trying to use these together:

babel.transform('import foo from \'bar.js\';', { plugins: [ 'transform-es2015-modules-systemjs', 'transform-system-register' ] });

Gives me the error:

TypeError: unknown: Source undefined is already a bundle file, so can't be built as a module.

[asapach]

It's used internally by Builder and is not really meant for public consumption. You're supposed to pass the module name as a transform parameter.
Although the error message could be better.