fix: add test case around empty response

This was actually just about configuring jQuery correctly to prevent
parsing the response as JSON. Setting the `dataType` to `text` does this
correctly.

Closes #315

tests/unit/mixins/ajax-request-test.js

@@ -19,6 +19,7 @@ import {
 } from 'ember-ajax/errors';
 import Pretender from 'pretender';
 import { jsonResponse, jsonFactory } from 'dummy/tests/helpers/json';
+import AjaxService from 'dummy/services/ajax';
 
 const {
   matchers: { anything, contains: matchContains }
@@ -790,6 +791,20 @@ describe('Unit | Mixin | ajax request', function() {
     });
   });
 
+  it('can handle an empty response', async function() {
+    this.server.post('/posts', () => [201, {}, undefined]);
+
+    const service = new AjaxService();
+
+    // NOTE: `dataType` must be set to `text`, otherwise jQuery will attempt
+    // to convert the response to JSON automatically
+    const response = await service.post('/posts', {
+      dataType: 'text'
+    });
+
+    expect(response).to.equal('');
+  });
+
   describe('URL building', function() {
     class NamespaceLeadingSlash extends AjaxRequest {
       static get slashType() {