code: def sku(self, product: str) -> Optional[str]:
      info = self._product_versions.get(product)
      if info:
          return info.sku
      return None
  
file_path: hail/batch/batch/driver/billing_manager.py
imports: import abc
  import logging
  from dataclasses import dataclass
  from typing import Dict, List, Optional
  from gear import Database, transaction
  from .pricing import Price
label_desc: Use image node_id 3 for calling the ProductVersions obj's underlying member method code with example usage: obj.sku(product) and returns: None, info