code: def _get_tensor(self, attr: TensorAttr) -> Optional[Tensor]:
      index, tensor = self.store.get(self.key(attr), (None, None))
  
      if tensor is None:
          return None
  
      assert isinstance(tensor, Tensor)
  
      # None indices return the whole tensor:
      if attr.index is None:
          return tensor
  
      # Empty slices return the whole tensor:
      if isinstance(attr.index, slice) and attr.index == slice(
          None, None, None
      ):
          return tensor
  
      assert isinstance(attr.index, Tensor)
  
      if attr.index.numel() == 0:
          return tensor[attr.index]
  
      idx = torch.cat(
          [(index == v).nonzero() for v in attr.index]
      ).view(-1)
      return tensor[idx]
  
file_path: pytorch_geometric/torch_geometric/testing/feature_store.py
imports: from typing import Dict, List, Optional, Tuple
  import torch
  from torch import Tensor
  from torch_geometric.data import FeatureStore, TensorAttr
  from torch_geometric.typing import FeatureTensorType
label_desc: Use image node_id 4 for calling the MyFeatureStore obj's underlying member method code with example usage: obj._get_tensor(attr) and returns: tensor, None, tensor, tensor, tensor