Fix exception changing player role

plugin/src/main/java/org/battleplugins/arena/competition/LiveCompetition.java

@@ -245,6 +245,23 @@ public final void leave(ArenaPlayer player, ArenaLeaveEvent.Cause cause) {
         player.remove();
     }
 
+    /**
+     * Changes the role of the player to the specified role.
+     *
+     * @param player the player to change the role of
+     * @param role the new role of the player
+     */
+    public final void changeRole(ArenaPlayer player, PlayerRole role) {
+        if (role == player.getRole()) {
+            return;
+        }
+
+        this.playersByRole.get(player.getRole()).remove(player);
+        this.playersByRole.computeIfAbsent(role, e -> new HashSet<>()).add(player);
+
+        player.setRole(role);
+    }
+
     /**
      * Gets all the {@link ArenaPlayer players} in the competition.
      *

plugin/src/main/java/org/battleplugins/arena/event/action/types/ChangeRoleAction.java

@@ -21,7 +21,7 @@ public ChangeRoleAction(Map<String, String> params) {
     public void call(ArenaPlayer arenaPlayer, Resolvable resolvable) {
         PlayerRole role = PlayerRole.valueOf(this.get(ROLE_KEY).toUpperCase(Locale.ROOT));
         boolean changedRole = arenaPlayer.getRole() != role;
-        arenaPlayer.setRole(role);
+        arenaPlayer.getCompetition().changeRole(arenaPlayer, role);
 
         if (changedRole && role == PlayerRole.SPECTATING) {
             arenaPlayer.getCompetition().getTeamManager().leaveTeam(arenaPlayer);