A similar fix is needed here to what was done at Kullanıcı_mesaj:Vito_Genovese/BDK.js#mw-panel_is_not_available_everywhere.
Something like:
/* initalise */
function npp_init() {
if (document.getElementById('mw-panel') === null) {
return;
}
// etc.
Thanks! --Amir E. Aharoni (mesaj) 11:51, 11 Mayıs 2017 (UTC)