Koenig - Fixed error in `{{clean-basic-html}}` when passed null/undefined

no issue
- default param was not protecting against null value being passed via helper params

lib/koenig-editor/addon/helpers/clean-basic-html.js

@@ -3,7 +3,7 @@ import {isArray} from '@ember/array';
 
 export function cleanBasicHtml(html = '') {
     if (isArray(html)) {
-        html = html[0];
+        html = html[0] || '';
     }
 
     let cleanHtml = html