Warning when registering plugin using baseDir if broccoli-rollup is installed

[jrjohnson]

When attempting to add a plugin

setupPreprocessorRegistry(type, registry) {
    registry.add('htmlbars-ast-plugin', {
      baseDir() {
        return __dirname;
      },
    });
  },

if broccoli-rollup is installed then when running ember serve I get the message:
Warning: failed to stat /preprocess-rollup/node_modules/broccoli-rollup/tmp/rollup-input_base_path-6obEeBLr.tmp/0

If I remove broccoli-rollup or remove the baseDir

setupPreprocessorRegistry(type, registry) {
    registry.add('htmlbars-ast-plugin', {});
},

Then no warning is printed.

This is reproducible in a brand new addon like https://github.com/jrjohnson/preprocess-rollup (addon doesn't do anything and the plugin itself won't work since it doesn't exist, bu the message is obvious.

I'm running into this while working on FortAwesome/ember-fontawesome#21