Solved storing custom items to config

So I have a problem when storing custom items into config, basically when the server shuts down all i save a HashMap that contains the player UUID as the key, and the object "MailStorage".

The MailStorage contains a list of HashMaps with a player UUID as the key and a List<ItemStack> as the value,
the thing is all works just fine if i store minecraft items and store them to config, the thing is if i store a custom item into the list of HashMaps all works well until i store them into config wich throws a:

Code:

Caused by: java.lang.NullPointerException: null key in entry: null=0

With any other minecraft item that doesnt happen.

Code:java

public void serializeStorage() {
 
        for(Entry<UUID, MailStorage> entry : mailStorage.entrySet()) {
            if(entry != null) {
                UUID playerUUID = entry.getKey();
                MailStorage storage = entry.getValue();
                YamlConfiguration config = plugin.getMailConfig();
                config.set("Storage." + playerUUID, storage.getStorage());
                plugin.saveMailConfig();
            }
 
 
        }
 
 
    }

 

@timtower I'm really confused right now , how i should check this ?

Here for example i get always "there arent null values":

Code:java

for(Entry<UUID, MailStorage> entry : mailStorage.entrySet()) {
            if(entry != null) {
                UUID playerUUID = entry.getKey();
                MailStorage storage = entry.getValue();
                YamlConfiguration config = plugin.getMailConfig();
                int nulls = 0;
 
                for(HashMap<String, List<ItemStack>> map : storage.getStorage()) {
 
                    for(Entry<String, List<ItemStack>> en : map.entrySet()) {
                        if(en.getValue() == null) {
                            nulls++;
                        }
                    }
 
                }
 
                if(nulls > 0) {
                    Bukkit.getConsoleSender().sendMessage(ChatColor.RED + "there are null values");
                } else {
                    Bukkit.getConsoleSender().sendMessage(ChatColor.GREEN + "there arent null values");
                }
 
 
 
                //config.set("Storage." + playerUUID, storage.getStorage());
                //plugin.saveMailConfig();
            }
 
 
        }

 

@timtower ok i'm a dummy, i just made the solution in the code above, just touched it a bit:

Code:java

public void serializeStorage() {
 
        for(Entry<UUID, MailStorage> entry : mailStorage.entrySet()) {
            if(entry != null) {
                UUID playerUUID = entry.getKey();
                MailStorage storage = entry.getValue();
                YamlConfiguration config = plugin.getMailConfig();
                int nulls = 0;
 
                for(HashMap<String, List<ItemStack>> map : storage.getStorage()) {
 
                    for(Entry<String, List<ItemStack>> en : map.entrySet()) {
                        if(en.getValue() == null) {
                            nulls++;
                        }
                    }
 
                }
 
                if(nulls == 0) {
                    config.set("Storage." + playerUUID, storage.getStorage());
                    plugin.saveMailConfig();
                }
 
            }
 
 
        }
 
 
    }