Fix sort-by with null values (#377)

* sort-by should sort null values last as well

`aValue.toLowerCase` throws an error if `null` is not explicitly handled:
`Uncaught TypeError: Cannot read property 'toLowerCase' of null`

* Improve sort-by undefined values test

Test that undefined values are sorted, not ignored

addon/helpers/sort-by.js

@@ -21,11 +21,11 @@ function sortDesc(key, a, b) {
   const aValue = get(a, key);
   const bValue = get(b, key);
 
-  if (typeof bValue == 'undefined') {
+  if (typeof bValue == 'undefined' || bValue === null) {
     // keep bValue last
     return -1;
   }
-  if (typeof aValue == 'undefined') {
+  if (typeof aValue == 'undefined' || aValue === null) {
     // put aValue last
     return 1;
   }
@@ -47,11 +47,11 @@ function sortAsc(key, a, b) {
   const aValue = get(a, key);
   const bValue = get(b, key);
 
-  if (typeof bValue == 'undefined') {
+  if (typeof bValue == 'undefined' || bValue === null) {
     // keep bValue last
     return -1;
   }
-  if (typeof aValue == 'undefined') {
+  if (typeof aValue == 'undefined' || aValue === null) {
     // put aValue last
     return 1;
   }

tests/integration/helpers/sort-by-test.js

@@ -301,21 +301,38 @@ module('Integration | Helper | {{sort-by}}', function(hooks) {
     assert.equal(find('*').textContent.trim(), 'abc', 'cab is sorted to abc');
   });
 
-  test('ignores undefined values sorting', async function (assert) {
+  test('it sorts undefined values last', async function(assert) {
     this.set('array', [
-      { name: 'c' },
-      { name: 'a' },
-      { name: undefined },
-      { name: 'b' },
+      { id: 1, name: 'c' },
+      { id: 2, name: 'a' },
+      { id: 3, name: undefined },
+      { id: 4, name: 'b' },
     ]);
 
     await render(hbs`
-      {{~#each (sort-by 'name' array) as |pet|~}}
-        {{~pet.name~}}
+      {{~#each (sort-by 'name' array) as |user|~}}
+        {{~user.id~}}
+      {{~/each~}}
+    `);
+
+    assert.equal(find('*').textContent.trim(), '2413');
+  });
+
+  test('it sorts null values last', async function(assert) {
+    this.set('array', [
+      { id: 1, name: 'c' },
+      { id: 2, name: 'a' },
+      { id: 3, name: null },
+      { id: 4, name: 'b' },
+    ]);
+
+    await render(hbs`
+      {{~#each (sort-by 'name' array) as |user|~}}
+        {{~user.id~}}
       {{~/each~}}
     `);
 
-    assert.equal(find('*').textContent.trim(), 'abc');
+    assert.equal(find('*').textContent.trim(), '2413');
   });
 
   test('It maintains order when values are the same', async function(assert) {