class_docstr: Skip connection with pre-activation, which includes BatchNorm3D and ReLU,
      in ResNet3D model (https://arxiv.org/abs/1603.05027).
code: def forward(self, x):
      if hasattr(self, "branch1_bn") and hasattr(self, "branch1_relu"):
          x = self.branch1_relu(self.branch1_bn(x))
      x = self.branch1(x)
      return x
  
imports: import torch.nn
  from .r2plus1_util import r2plus1_unit
label_desc: Use image node_id 2 for calling the PreactivatedShortcutTransformation obj's underlying member method code with example usage: obj.forward(x) and returns: x