adjust

src/client/js/components/Admin/Customize/CustomizeHeaderSetting.jsx

@@ -60,7 +60,7 @@ class CustomizeHeaderSetting extends React.Component {
         <div className="col-xs-12">
           <CustomHeaderEditor
             // The value passed must be immutable
-            value={appContainer.config.customizeHeader}
+            value={appContainer.config.customizeHeader || ''}
             onChange={(inputValue) => { adminCustomizeContainer.changeCustomizeHeader(inputValue) }}
           />
         </div>