The relation packet was not meant to be sent to a GM.
Read the warning.
If you do not want to get information about what is going on...
Index: java/org/l2jmobius/gameserver/network/serverpackets/RelationChanged.java
===================================================================
--- java/org/l2jmobius/gameserver/network/serverpackets/RelationChanged.java (revision 10070)
+++ java/org/l2jmobius/gameserver/network/serverpackets/RelationChanged.java (working copy)
@@ -77,7 +77,7 @@
{
if (activeChar.isInvisible())
{
- throw new IllegalArgumentException("Cannot add insivisble character to multi relation packet");
+ return;
}
final Relation r = new Relation();
r._objId = activeChar.getObjectId();