code: def forward(self, x, batch):
      return self.aggr(x, batch, dim=0)
  
imports: import torch
  from torch_geometric.nn import SumAggregation
  from torch_geometric.nn.to_fixed_size_transformer import to_fixed_size
label_desc: Use image node_id 2 for calling the Model obj's underlying member method code with example usage: obj.forward(x, batch) and returns: self