Error when trying to summon entity:

[12:09:12] [Server thread/WARN] [minecraft/EntityType]: Exception loading entity: 
java.lang.NullPointerException: Cannot invoke "net.minecraft.network.syncher.SynchedEntityData$DataItem.getValue()" because "dataitem" is null

I followed these docs to create what I have below in my entity class:

public abstract class Dinosaur extends Animal {
    
    static final EntityDataAccessor<Integer> serum = SynchedEntityData.defineId(Dinosaur.class, EntityDataSerializers.INT);
    
    protected Dinosaur(EntityType<? extends Animal> e, Level l) {
        super(e, l);
    }
    
    public boolean isJuvenile() {
        return this.isBaby() && this.getSerum() > 0;
    }
    
    @Override
    public void tick() {
        super.tick();
        if (this.getSerum() >= 4) {
            this.age = 0;
            if (this.isBaby()) {
                this.setBaby(false);
            }
        }
        else {
            if (!this.isBaby()) {
                this.setBaby(true);
            }
            this.age = -20;
        }
    }
    
    @Override
    public void defineSynchedData() {
        this.entityData.define(serum, 1);
    }
    
    public void addSerum() {
        int s = this.getSerum();
        this.getEntityData().set(serum, s++);
    }
    
    public int getSerum() {
        return this.getEntityData().get(serum);
    }

}

Any help is greatly appreciated, thank you

Forgot to call defineSynchedData's super method. Case closed.

wdym?I'm having this issue as well

me too, but in my case, the EntityDataAccessor is null

Edited September 8, 20232 yr by btuh