[HELP] NPC Disappearing

My NPC disappear with time , where it can be the error ?

Are you using MoopleDEV?

Npc's should naturally despawn if they are out of range, if it's been coded into the source.

Beyond That I'm Quest Problems , mobs stop drop and rise.

I'm using this in MapleQuestRequiremnt

case MOB:
for (MapleData mobEntry : getData().getChildren()) {
int mobId = MapleDataTool.getInt(mobEntry.getChildByPath("id"));
int killReq = MapleDataTool.getInt(mobEntry.getChildByPath("count"));
try {
if (c.getQuest(quest).getMobKills(mobId) < killReq) {
return false;
}
} catch (Exception e) {
continue;
}
}
return true;


it is ending the server : /