use confirmedArrays when performing intersect (#384)

addon/helpers/intersect.js

@@ -7,9 +7,9 @@ export function intersect([...arrays]) {
   });
   // copied from https://github.com/emberjs/ember.js/blob/315ec6472ff542ac714432036cc96fe4bd62bd1f/packages/%40ember/object/lib/computed/reduce_computed_macros.js#L1063-L1100
   let results = confirmedArrays.pop().filter(candidate => {
-    for (let i = 0; i < arrays.length; i++) {
+    for (let i = 0; i < confirmedArrays.length; i++) {
       let found = false;
-      let array = arrays[i];
+      let array = confirmedArrays[i];
       for (let j = 0; j < array.length; j++) {
         if (array[j] === candidate) {
           found = true;

tests/integration/helpers/intersect-test.js

@@ -51,4 +51,18 @@ module('Integration | Helper | {{intersect}}', function(hooks) {
 
     assert.equal(find('*').textContent.trim(), 'this is all that will render', 'no error is thrown');
   });
+
+  test('it allows a first parameter null array', async function(assert) {
+    this.set('array1', null);
+    this.set('array2', ['foo', 'baz']);
+
+    await render(hbs`
+      this is all that will render
+      {{#each (intersect array1 array2) as |value|}}
+        {{value}}
+      {{/each}}
+    `);
+
+    assert.equal(find('*').textContent.trim(), 'this is all that will render', 'no error is thrown');
+  });
 });