code: def __post_init__(self) -> None:
      self.optional_field_exist: Dict[str, bool] = {
          f: False for f in get_optional_fields(Transition)
      }
  
imports: from abc import ABC, abstractmethod
  from dataclasses import asdict, dataclass, field, fields
  from typing import Any, Callable, Dict, List, Optional, Union
  import numpy
  import reagent.core.types
  import torch
  import torch.nn.functional
label_desc: Use image node_id 1 for calling the Trajectory obj's underlying member method code with example usage: obj.__post_init__() without return types