ItemBuilder

import io.github.chi2l3s.nextlib.api.item.ItemBuilder;
import io.github.chi2l3s.nextlib.api.item.ItemUtil;
import org.bukkit.Material;
import org.bukkit.enchantments.Enchantment;
import org.bukkit.inventory.ItemStack;

ItemStack item = new ItemBuilder(Material.DIAMOND_SWORD)
  .setName("&b&lLegendary Sword")
  .setLore(java.util.List.of("&7A powerful weapon", "&7+10 Damage"))
  .addEnchant(Enchantment.DAMAGE_ALL, 5, true)
  .setUnbreakable(true)
  .setPersistentData(this, "custom_id", "legend_sword")
  .build();

boolean hasTag = ItemUtil.hasPersistentData(item, this, "custom_id");