Program: 179089
Project: 179089
Buggy source:
public void onPlayerInteract(PlayerInteractEvent event){
  if (event.getAction() == Action.RIGHT_CLICK_BLOCK) {
    Player player=event.getPlayer();
    if (User.getUser(plugin,player).hasPerm("String_Node_Str") && player.getItemInHand().getType() == Material.WOOD_SPADE) {
      checkPlayer(player.getName());
      if (this.corner.get(player.getName()).corner2 != event.getClickedBlock().getLocation()) {
        this.corner.get(player.getName()).setCorner2(event.getClickedBlock().getLocation());
        Location corner2=this.corner.get(player.getName()).getCorner2();
        player.sendMessage(ChatColor.LIGHT_PURPLE + "String_Node_Str" + corner2.getX()+ "String_Node_Str"+ corner2.getY()+ "String_Node_Str"+ corner2.getZ()+ "String_Node_Str"+ corner2.getWorld().getName()+ "String_Node_Str");
      }
      return;
    }
  }
 else   if (event.getAction() == Action.LEFT_CLICK_BLOCK) {
    Player player=event.getPlayer();
    if (User.getUser(plugin,player).hasPerm("String_Node_Str") && player.getItemInHand().getType() == Material.WOOD_SPADE) {
      checkPlayer(player.getName());
      if (this.corner.get(player.getName()).corner1 != event.getClickedBlock().getLocation()) {
        this.corner.get(player.getName()).setCorner1(event.getClickedBlock().getLocation());
        Location corner1=this.corner.get(player.getName()).getCorner1();
        player.sendMessage(ChatColor.LIGHT_PURPLE + "String_Node_Str" + corner1.getX()+ "String_Node_Str"+ corner1.getY()+ "String_Node_Str"+ corner1.getZ()+ "String_Node_Str"+ corner1.getWorld().getName()+ "String_Node_Str");
      }
      return;
    }
  }
}

Fixed version (ground truth):
public void onPlayerInteract(PlayerInteractEvent event){
  if (event.getAction() == Action.RIGHT_CLICK_BLOCK) {
    Player player=event.getPlayer();
    if (User.getUser(plugin,player).hasPerm("String_Node_Str") && player.getItemInHand().getType() == Material.WOOD_SPADE) {
      checkPlayer(player.getName());
      if (this.corner.get(player.getName()).corner2set) {
        if (this.corner.get(player.getName()).corner2.equals(event.getClickedBlock().getLocation())) {
          return;
        }
      }
      this.corner.get(player.getName()).setCorner2(event.getClickedBlock().getLocation());
      Location corner2=this.corner.get(player.getName()).getCorner2();
      player.sendMessage(ChatColor.LIGHT_PURPLE + "String_Node_Str" + corner2.getX()+ "String_Node_Str"+ corner2.getY()+ "String_Node_Str"+ corner2.getZ()+ "String_Node_Str"+ corner2.getWorld().getName()+ "String_Node_Str");
    }
    return;
  }
 else   if (event.getAction() == Action.LEFT_CLICK_BLOCK) {
    Player player=event.getPlayer();
    if (User.getUser(plugin,player).hasPerm("String_Node_Str") && player.getItemInHand().getType() == Material.WOOD_SPADE) {
      checkPlayer(player.getName());
      if (this.corner.get(player.getName()).corner1set) {
        if (this.corner.get(player.getName()).corner1.equals(event.getClickedBlock().getLocation())) {
          return;
        }
      }
      this.corner.get(player.getName()).setCorner1(event.getClickedBlock().getLocation());
      Location corner1=this.corner.get(player.getName()).getCorner1();
      player.sendMessage(ChatColor.LIGHT_PURPLE + "String_Node_Str" + corner1.getX()+ "String_Node_Str"+ corner1.getY()+ "String_Node_Str"+ corner1.getZ()+ "String_Node_Str"+ corner1.getWorld().getName()+ "String_Node_Str");
    }
    return;
  }
}