update dig to return immediately if object passed in is null

src/helpers/dig.js

@@ -1,6 +1,7 @@
 'use strict'
 
 module.exports = (object, path) => {
+  if (object == null) return
   const paths = path.split('.')
   let result = object
   for (let i = 0, len = paths.length; i < len; i++) {