don't save null value if no value is provided

fixes PLAT-1762

test plan:
* Add a manual external app
* Enter valid settings but leave the description and domain blank
* Save the app
* Edit the same app and save again
* Edit and ensure the domain and description are not "null"

Change-Id: I7046ef564790acd8ae790c42611d832ae9f803e6
Reviewed-on: https://gerrit.instructure.com/88861
Reviewed-by: Pedro Fajardo <pfajardo@instructure.com>
Tested-by: Jenkins
QA-Review: Benjamin Christian Nelson <bcnelson@instructure.com>
Reviewed-by: Andrew Butterfield <abutterfield@instructure.com>
Product-Review: August Thornton <august@instructure.com>

app/jsx/external_apps/components/ConfigurationFormManual.jsx

@@ -130,7 +130,7 @@ define([
               <TextInput
                 ref="domain"
                 id="domain"
-                defaultValue={this.props.domain}
+                defaultValue={this.props.domain ? this.props.domain : ''}
                 label={I18n.t('Domain')}
                 errors={this.state.errors} />
             </div>
@@ -157,7 +157,7 @@ define([
           <TextAreaInput
             ref="description"
             id="description"
-            defaultValue={this.props.description}
+            defaultValue={this.props.description ? this.props.description : ''}
             label={I18n.t('Description')}
             rows={6}
             errors={this.state.errors} />

spec/javascripts/jsx/external_apps/components/ConfigurationFormManualSpec.jsx

@@ -0,0 +1,42 @@
+define([
+  'react',
+  'jsx/external_apps/components/ConfigurationFormManual'
+], (React, ConfigurationFormManual) => {
+
+  const TestUtils = React.addons.TestUtils;
+
+  module('External Apps Manual Configuration Form');
+
+  const fakeStore = {
+    findAppByShortName () {
+      return {
+        short_name: 'someApp',
+        config_options: []
+      };
+    }
+  };
+
+  const component = TestUtils.renderIntoDocument (
+    <ConfigurationFormManual
+      domain=''
+      description=''
+      shortName="someApp"
+      store={fakeStore}
+    />
+  );
+
+    test('domain field should not be null', () => {
+
+      const app = TestUtils.findRenderedComponentWithType(component, ConfigurationFormManual);
+
+      equal(app.props.domain, '');
+    });
+
+    test('description field should not be null', () => {
+
+      const app = TestUtils.findRenderedComponentWithType(component, ConfigurationFormManual);
+
+      equal(app.props.description, '');
+    });
+
+});