That error is caused by the following bit of code in src/plugins.js
paths = paths.map(function(pluginLib) { var parent = path.dirname(pluginLib); return cached.filter(function(libPath) { return libPath.indexOf(parent) !== -1; }); }).reduce(function(prev, cur) { return prev.concat(cur); });If paths is an empty array calling reduce will throw that error. We should add better checks to detect that.