Merge pull request #4 from joelalejandro/fix/issue-3

Adds null check to transform

Author: Joel Alejandro Villarreal Bertoldi

index.js

@@ -1,7 +1,7 @@
 'use strict';
 
 function csvToArray(value) {
-  return value.split(',').map(function(item) { return item.trim(); });
+  return value !== null ? value.split(',').map(function(item) { return item.trim(); }) : [];
 }
 
 function applyCsvToArrayTransform(data, model) {
@@ -30,4 +30,4 @@ module.exports = function (options = {}) { // eslint-disable-line no-unused-vars
     }
     return Promise.resolve(hook);
   };
-};
+};