code: def _build(
      loss_fn: Optional[Callable] = None,
      metrics: Union[
          torchmetrics.Metric, Mapping, Sequence, None
      ] = None,
  ):
      metrics = metrics or torchmetrics.MeanSquaredError()
      loss_fn = loss_fn or F.mse_loss
  
      return metrics, loss_fn
  
file_path: lightning-flash/src/flash/core/regression.py
imports: from typing import Callable, Mapping, Optional, Sequence, Union
  import torch.nn.functional
  import torchmetrics
  from torch import Tensor
  from flash.core.adapter import AdapterTask
  from flash.core.model import Task
label_desc: Use image node_id 1 for calling the RegressionMixin obj's underlying member method code with example usage: obj._build(loss_fn, metrics) and returns: metrics,  loss_fn