copy NBTModifier temporary to start working on a fix for 1.20.6

src/main/java/me/hsgamer/bettergui/builder/ItemModifierBuilder.java

@@ -1,5 +1,6 @@
 package me.hsgamer.bettergui.builder;
 
+import me.hsgamer.bettergui.modifier.NBTModifier;
 import me.hsgamer.hscore.builder.MassBuilder;
 import me.hsgamer.hscore.bukkit.item.modifier.*;
 import me.hsgamer.hscore.minecraft.item.ItemModifier;

src/main/java/me/hsgamer/bettergui/modifier/NBTModifier.java

@@ -0,0 +1,47 @@
+package me.hsgamer.bettergui.modifier;
+
+import com.google.gson.Gson;
+import me.hsgamer.hscore.common.StringReplacer;
+import me.hsgamer.hscore.common.Validate;
+import me.hsgamer.hscore.minecraft.item.ItemModifier;
+import org.bukkit.Bukkit;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Collection;
+import java.util.Map;
+import java.util.Objects;
+import java.util.UUID;
+
+public class NBTModifier implements ItemModifier<ItemStack> {
+  private static final Gson GSON = new Gson();
+  private String nbtData = "";
+
+  @SuppressWarnings("deprecation")
+  @Override
+  public @NotNull ItemStack modify(@NotNull ItemStack original, UUID uuid, @NotNull Collection<StringReplacer> stringReplacers) {
+    if (Validate.isNullOrEmpty(nbtData)) {
+      return original;
+    }
+    try {
+      return Bukkit.getUnsafe().modifyItemStack(original, StringReplacer.replace(nbtData, uuid, stringReplacers));
+    } catch (Throwable throwable) {
+      return original;
+    }
+  }
+
+  @Override
+  public Object toObject() {
+    return nbtData;
+  }
+
+  @Override
+  public void loadFromObject(Object object) {
+    if (object instanceof Map) {
+      Map<?, ?> map = (Map<?, ?>) object;
+      this.nbtData = GSON.toJson(map);
+    } else {
+      this.nbtData = Objects.toString(object, "");
+    }
+  }
+}