Updating for Mongoose 5.6.13+

The method `pathType` can't handle undefined anymore. So do an extra filter

Author: makinde

src/getAuthorizedFields.js

@@ -6,6 +6,7 @@ function getAuthorizedFields(schema, authLevels, action) {
 
   return _.chain(cleanedLevels)
     .flatMap(level => schema.permissions[level][action])
+    .filter() // schema.pathType can't handle undefined values anymore (mongoose gh-6405)
     .filter(path => schema.pathType(path) !== 'adhocOrUndefined') // ensure fields are in schema
     .uniq() // dropping duplicates
     .value();