fix(toJSON): handle null properties

helpers/toJSON.js

@@ -3,9 +3,9 @@ function toJSON (form) {
     return Object.keys(object).reduce(function (newObject, key) {
       if (Array.isArray(object[key])) {
         newObject[key] = extractArray(object[key])
-      } else if ('value' in object[key]) {
+      } else if (object[key] && 'value' in object[key]) {
         newObject[key] = object[key].value
-      } else {
+      } else if (object[key] && typeof object[key] === 'object') {
         newObject[key] = extractObject(object[key])
       }
       return newObject

tests/toJSON.js

@@ -0,0 +1,27 @@
+var toJSON = require('../helpers/toJSON')
+var Form = require('../Form')
+
+module.exports = {
+  setUp: function (callback) {
+    this.form = Form({
+      name: {
+        value: 'foo'
+      },
+      name2: {
+        value: 'bar'
+      }
+    })
+    callback()
+  },
+  tearDown: function (callback) {
+    callback()
+  },
+  testToJSON: function (test) {
+    this.form.name3 = null;
+    test.deepEqual(toJSON(this.form), {
+      name: 'foo',
+      name2: 'bar'
+    })
+    test.done()
+  }
+}