fix checkbox name binding exception if model value is not an array in…

… certain circumstances

the test doesn't fail without the fix, but the fix definitely fixes a
bug that happens with the exact same template construct elsewhere

src/view/items/element/binding/CheckboxNameBinding.js

@@ -68,7 +68,8 @@ export default class CheckboxNameBinding extends Binding {
 
   handleChange() {
     this.isChecked = this.element.node.checked;
-    this.group.value = this.model.get().slice();
+    const mval = this.model.get();
+    this.group.value = mval === undefined ? [] : mval.slice();
     const value = this.element.getAttribute('value');
     if (this.isChecked && !this.arrayContains(this.group.value, value)) {
       this.group.value.push(value);

tests/browser/twoway.js

@@ -232,6 +232,20 @@ export default function() {
     t.ok(!ractive.find('#green').checked);
   });
 
+  test('Checkbox name bindings with an undefined nested name will build an array', t => {
+    const r = new Ractive({
+      el: fixture,
+      template: `{{#each paths as path}}{{#each colors as color}}<input id="{{.}}" type=checkbox name="{{~/foo[path]}}" value="{{.}}" />{{/each}}{{/each}}`,
+      data: {
+        paths: ['colors'],
+        colors: ['red', 'green', 'blue']
+      }
+    });
+
+    fire(r.find('#green'), 'click');
+    t.deepEqual(r.get('foo.colors'), ['green']);
+  });
+
   test('Checkbox Name bindings use property attributes to determined if checked or not', t => {
     let ractive = new Ractive({
       el: fixture,