code: def forward(self, input, encoder_state, incr_state=None):
      # our CK Encoder returns an extra output which the Transformer decoder
      # doesn't expect (the knowledge selection mask). Just chop it off
      encoder_output, encoder_mask, _ = encoder_state
      return self.transformer(
          input, (encoder_output, encoder_mask), incr_state
      )
  
file_path: ParlAI/projects/wizard_of_wikipedia/generator/modules.py
imports: from typing import Dict
  import numpy
  import torch
  import torch.nn
  from parlai.utils.torch import neginf
  from parlai.agents.transformer.modules import TransformerGeneratorModel
label_desc: Use image node_id 2 for calling the ContextKnowledgeDecoder obj's underlying member method code with example usage: obj.forward(input, encoder_state, incr_state) and returns: self