public String createSubForum(User invoker ,User moderator, String subForumName) {
		if (!invoker.hasPermission(Permissions.CREATE_SUB_FORUM) || !TextVerifier.verifyName(subForumName, new Policy()) || moderator == null) return null;
		
		SubForum newSF = new SubForum(subForumName, moderator);
		subForums.add(newSF);
		save();
		return newSF.getId();
	}