Program: 34069
Project: 34069
Buggy source:
@EventHandler(priority=EventPriority.LOWEST,ignoreCancelled=false) public void onPlayerPortal(PlayerPortalEvent event){
  if (!Settings.createNether) {
    return;
  }
  if (event.isCancelled()) {
    return;
  }
  Location currentLocation=event.getFrom().clone();
  String currentWorld=currentLocation.getWorld().getName();
  if (!currentWorld.equalsIgnoreCase(Settings.worldName) && !currentWorld.equalsIgnoreCase(Settings.worldName + "String_Node_Str") && !currentWorld.equalsIgnoreCase(Settings.worldName + "String_Node_Str")) {
    return;
  }
  if (!Settings.allowPortalUse && currentWorld.equalsIgnoreCase(Settings.worldName)) {
    if (!event.getPlayer().isOp() && !VaultHelper.checkPerm(event.getPlayer(),Settings.PERMPREFIX + "String_Node_Str")) {
      if (!plugin.getGrid().locationIsOnIsland(event.getPlayer(),event.getPlayer().getLocation()) && !plugin.getGrid().isAtSpawn(event.getPlayer().getLocation())) {
        event.getPlayer().sendMessage(ChatColor.RED + Locale.islandProtected);
        event.setCancelled(true);
        return;
      }
    }
  }
  Location destination=plugin.getGrid().getSafeHomeLocation(event.getPlayer().getUniqueId());
  if (destination == null) {
    event.getPlayer().sendMessage(ChatColor.YELLOW + "String_Node_Str" + Settings.ISLANDCOMMAND+ "String_Node_Str");
    event.setCancelled(true);
    return;
  }
  if (currentWorld.equalsIgnoreCase(Settings.worldName)) {
    if (plugin.getServer().getWorld(Settings.worldName + "String_Node_Str") != null) {
      if (event.getCause().equals(TeleportCause.END_PORTAL)) {
        event.setCancelled(true);
        Location end_place=plugin.getServer().getWorld(Settings.worldName + "String_Node_Str").getSpawnLocation();
        if (GridManager.isSafeLocation(end_place)) {
          event.getPlayer().teleport(end_place);
          return;
        }
 else {
          event.getPlayer().sendMessage(ChatColor.RED + Locale.warpserrorNotSafe);
          plugin.getGrid().homeTeleport(event.getPlayer());
          return;
        }
      }
    }
    UUID playerUUID=event.getPlayer().getUniqueId();
    World world=plugin.getServer().getWorld(Settings.worldName + "String_Node_Str");
    if (Settings.newNether) {
      Location netherHome=null;
      if (plugin.getPlayers().inTeam(playerUUID)) {
        netherHome=plugin.getPlayers().getTeamIslandLocation(playerUUID).toVector().toLocation(world);
      }
 else {
        netherHome=plugin.getPlayers().getIslandLocation(playerUUID).toVector().toLocation(world);
      }
      if (netherHome == null) {
        event.setCancelled(true);
        return;
      }
      event.setTo(netherHome);
    }
 else {
      event.setTo(plugin.getServer().getWorld(Settings.worldName + "String_Node_Str").getSpawnLocation());
    }
    event.useTravelAgent(true);
  }
 else {
    event.setTo(destination);
    event.useTravelAgent(false);
  }
}

Fixed version (ground truth):
@EventHandler(priority=EventPriority.LOWEST,ignoreCancelled=false) public void onPlayerPortal(PlayerPortalEvent event){
  if (!Settings.createNether) {
    return;
  }
  if (event.isCancelled()) {
    return;
  }
  Location currentLocation=event.getFrom().clone();
  String currentWorld=currentLocation.getWorld().getName();
  if (!currentWorld.equalsIgnoreCase(Settings.worldName) && !currentWorld.equalsIgnoreCase(Settings.worldName + "String_Node_Str") && !currentWorld.equalsIgnoreCase(Settings.worldName + "String_Node_Str")) {
    return;
  }
  if (!Settings.allowPortalUse && currentWorld.equalsIgnoreCase(Settings.worldName)) {
    if (!event.getPlayer().isOp() && !VaultHelper.checkPerm(event.getPlayer(),Settings.PERMPREFIX + "String_Node_Str")) {
      if (!plugin.getGrid().locationIsOnIsland(event.getPlayer(),event.getPlayer().getLocation()) && !plugin.getGrid().isAtSpawn(event.getPlayer().getLocation())) {
        event.getPlayer().sendMessage(ChatColor.RED + Locale.islandProtected);
        event.setCancelled(true);
        return;
      }
    }
  }
  Location destination=plugin.getGrid().getSafeHomeLocation(event.getPlayer().getUniqueId());
  if (destination == null) {
    event.getPlayer().sendMessage(ChatColor.YELLOW + "String_Node_Str" + Settings.ISLANDCOMMAND+ "String_Node_Str");
    event.setCancelled(true);
    return;
  }
  if (currentWorld.equalsIgnoreCase(Settings.worldName)) {
    if (plugin.getServer().getWorld(Settings.worldName + "String_Node_Str") != null) {
      if (event.getCause().equals(TeleportCause.END_PORTAL)) {
        event.setCancelled(true);
        Location end_place=plugin.getServer().getWorld(Settings.worldName + "String_Node_Str").getSpawnLocation();
        if (GridManager.isSafeLocation(end_place)) {
          event.getPlayer().teleport(end_place);
          return;
        }
 else {
          event.getPlayer().sendMessage(ChatColor.RED + Locale.warpserrorNotSafe);
          plugin.getGrid().homeTeleport(event.getPlayer());
          return;
        }
      }
    }
    UUID playerUUID=event.getPlayer().getUniqueId();
    World world=plugin.getServer().getWorld(Settings.worldName + "String_Node_Str");
    if (Settings.newNether) {
      Location netherHome=null;
      if (plugin.getPlayers().inTeam(playerUUID)) {
        netherHome=plugin.getPlayers().getTeamIslandLocation(playerUUID).toVector().toLocation(world);
      }
 else {
        netherHome=plugin.getPlayers().getIslandLocation(playerUUID).toVector().toLocation(world);
      }
      if (netherHome == null) {
        event.setCancelled(true);
        return;
      }
      event.setTo(netherHome);
    }
 else {
      event.setTo(plugin.getServer().getWorld(Settings.worldName + "String_Node_Str").getSpawnLocation());
    }
    event.useTravelAgent(true);
  }
 else {
    if (plugin.getServer().getWorld(Settings.worldName + "String_Node_Str") != null) {
      if (event.getCause().equals(TeleportCause.END_PORTAL)) {
        event.setCancelled(true);
        Location end_place=plugin.getServer().getWorld(Settings.worldName + "String_Node_Str").getSpawnLocation();
        if (GridManager.isSafeLocation(end_place)) {
          event.getPlayer().teleport(end_place);
          return;
        }
 else {
          event.getPlayer().sendMessage(ChatColor.RED + Locale.warpserrorNotSafe);
          plugin.getGrid().homeTeleport(event.getPlayer());
          return;
        }
      }
    }
    event.setTo(destination);
    event.useTravelAgent(false);
  }
}