Blocking js error on App Within Minutes

To reproduce this issue :
1) Log in as administrator
2) Create an application with App With Minute
3) Create an application entry
4) Edit the entry
5) On the edit page of the entry when I click everywhere on the page I have the following Javascript error :

Uncaught TypeError: Cannot read property 'addClassName' of null
Uncaught TypeError: Cannot read property 'addClassName' of nullxwiki-min.js?defer=false&language=en:1 exwiki-min.js?defer=false&language=en:1 (anonymous function)prototype.js:15 (anonymous function)

This error is blocking my javascript code.