public class ArraySet<T> {
    private T[] items;
    private int size;

    public ArraySet() {
        items = (T[]) new Object[100];
        size = 0;
    }

    public void add(T value) {
        for (int i = 0; i < size; i++) {
            if (items[i] == value) {
                return;
            }
        }
        items[size + 1] = value;
        size ++;
    }

    public boolean contains(T x) {
        for (int i = 0; i < size; i++) {
            if (items[i].equals(x)) {
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {
        ArraySet<String> s = new ArraySet<>();
        // test add function
        s.add("horse");
        System.out.println(s.size);
        s.add("fish");
        System.out.println(s.size);
        // test contains function
        System.out.println(s.contains("horse"));
    }
}

I self create an Arrayset class to store strings with add function and contains function, but the contains function goes wrong. I try to modify my add function but it doesn't works.

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Object.equals(Object)" because "this.items[i]" is null

https://pastebin.com/vtcMwSRn

So I am currently going crazy trying to get images to load when you export it to a .jar file. Before I was just using, "new imageicon("picturepath")"

As you can see from lines 30-34.

Then I found out that doesn't carry over when you make the project into a .jar file, okay cool. So I found out that you want to use, "getResource" okay cool got it. Try that and now I get the error in the title. when that location isn't fucking null so that's horse shit. I've tried every variation of that path. I have tried moving my images folder all over the project; from inside the src folder, where it is now, to just in the main project folder, etc. I don't know why it isn't happy.

Exception in thread "main" java.lang.NullPointerException: Cannot invoke 
"java.net.URL.toExternalForm()" because "location" is null
at java.desktop/javax.swing.ImageIcon.<init>(ImageIcon.java:234)
at LaunchPage.<init>(LaunchPage.java:25)
at Main.main(Main.java:5)

when people try to connect to my server, they receive this error message
internal exception java.lang.nullpointerexception can not invoke "net.minecraft.nbt.compoundtag.m_128459_(string)

i also received this error message as well but during this test for some reason it let me join the server, i've tested this out on singleplayer as well and the world works fine nothing seems to be corrupted it just doesn't work for the server.
we've also made multiple worlds for this specific pack i've made and they all have had this problem, randomly sometimes people will be able to join and play normally but other times they get this error and they cant play.
friends latest.log: https://mclo.gs/mHmks83
servers lastest.log: https://mclo.gs/si9AJk2