spawn_egg register

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ModItem

  public static final RegistryObject<Item> STRAWBERRY_COW_SPAWN_EGG = ITEMS.register("strawberry_cow_spawn_egg", () -> new ModSpawnEgg(ModEntity.STRAWBERRY_COW, 0xF5ABC5, 0xFFD7E5, new Item.Properties().group(MysticsBiomes.TAB)));
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ModSpawnEgg

public class ModSpawnEgg extends SpawnEggItem {

    protected final static List<ModSpawnEgg> UNADDED_EGGS = new ArrayList<>();
    private final Lazy<? extends EntityType<?>> entityTypeSupplier;

    public ModSpawnEgg(final RegistryObject<? extends EntityType<?>> entityTypeSupplier, int primaryColorIn, int secondaryColorIn, Properties builder) {
        super(null, primaryColorIn, secondaryColorIn, builder);
        this.entityTypeSupplier = Lazy.of(entityTypeSupplier::get);
        UNADDED_EGGS.add(this);
    }

    public static void initSpawnEgg() {
        final Map<EntityType<?>, SpawnEggItem> EGGS = ObfuscationReflectionHelper.getPrivateValue(SpawnEggItem.class, null, "field_195987_b");
        DefaultDispenseItemBehavior dispenseBehavior = new DefaultDispenseItemBehavior() {

            @Override
            protected ItemStack dispenseStack(IBlockSource source, ItemStack stack) {
                Direction direction = source.getBlockState().get(DispenserBlock.FACING);
                EntityType<?> type = ((SpawnEggItem) stack.getItem()).getType(stack.getTag());
                type.spawn(source.getWorld(), stack, null, source.getBlockPos(),
                        SpawnReason.DISPENSER, direction != Direction.UP, false);
                stack.shrink(1);
                return stack;
            }
        };

        for (final SpawnEggItem spawnEgg : UNADDED_EGGS) {
            EGGS.put(spawnEgg.getType(null), spawnEgg);
            DispenserBlock.registerDispenseBehavior(spawnEgg, dispenseBehavior);
        }
        UNADDED_EGGS.clear();
    }

    @Override
    public EntityType<?> getType(CompoundNBT nbt) {
        return this.entityTypeSupplier.get();
    }
}
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ClientEventBusSubscriber

@SubscribeEvent
    public static void onRegisterEntities(final RegistryEvent.Register<EntityType<?>> event) {
        ModSpawnEgg.initSpawnEgg();
    }