code: def forward(self, unpooled):
      # [batch_size, length, hidden_dim]
      assert len(unpooled.shape) == 3
      return unpooled[:, 0]
  
imports: from __future__ import annotations
  import abc
  import torch
  import torch.nn
  import transformers
  from jiant.ext.allennlp import SelfAttentiveSpanExtractor
  from jiant.shared.model_resolution import ModelArchitectures
  from jiant.tasks.core import TaskTypes
  from typing import Callable
  from typing import List
label_desc: Use image node_id 2 for calling the FirstPoolerHead obj's underlying member method code with example usage: obj.forward(unpooled) and returns: unpooled