Fixing the fact that the addon-docs ember framework wasn't outputting the default value properly

addons/docs/src/frameworks/ember/jsondoc.js

@@ -14,7 +14,7 @@ export const extractArgTypes = (componentName) => {
   const rows = componentDoc.attributes.arguments.map((prop) => {
     return {
       name: prop.name,
-      defaultValue: prop.defaultValue,
+      defaultValue: { summary: prop.defaultValue },
       description: prop.description,
       table: {
         type: {

examples/ember-cli/app/components/welcome-banner.js

@@ -23,6 +23,7 @@ export default Component.extend({
    * The hex-formatted color code for the background.
    * @argument backgroundColor
    * @type {string}
+   * @default null
    */
   backgroundColor: null,