class_docstr: A base class to support exporting through ONNX
docstr: This function provides the input for ONNX graph tracing.
  
  The return value should be what expected by `forward()`.
code: def input_prototype(self) -> Any:
      """
      This function provides the input for ONNX graph tracing.
  
      The return value should be what expected by `forward()`.
      """
      raise NotImplementedError
  
file_path: ReAgent/reagent/models/base.py
imports: from copy import deepcopy
  from typing import Any, Optional
  import torch.nn
  from reagent.core import types
label_desc: Use image node_id 1 for calling the ModelBase obj's underlying member method code with example usage: obj.input_prototype() without return types