Coerce features to string

lib/common/parse-features-string.js

@@ -2,6 +2,7 @@
 // - `features` input string
 // - `emit` function(key, value) - called for each parsed KV
 module.exports = function parseFeaturesString (features, emit) {
+  features = `${features}`
   // split the string by ','
   features.split(/,\s*/).forEach((feature) => {
     // expected form is either a key by itself or a key/value pair in the form of