class_docstr: Head of GNN, graph prediction
  
  The optional post_mp layer (specified by cfg.gnn.post_mp) is used
  to transform the pooled embedding using an MLP.
class_docstr_tok: ["Head","of","GNN",",","graph","prediction","The","optional","post_mp","layer","(","specified","by","cfg.gnn.post_mp",")","is","used","to","transform","the","pooled","embedding","using","an","MLP","."]
code: def _apply_index(self, batch):
      return batch.graph_feature, batch.y
  
imports: import torch
  import torch.nn
  import graphgym.register
  from graphgym.config import cfg
  from graphgym.models.layer_pyg import MLP
  from graphgym.models.pooling import pooling_dict
label_desc: Use image node_id 2 for calling the GNNGraphHead obj's underlying member method code with example usage: obj._apply_index(batch) and returns: batch,  batch