code: def forward(self, pred: paddle.Tensor, gt, mask):
      loss = (paddle.abs(pred - gt) * mask).sum() / (
          mask.sum() + self.eps
      )
      return loss
  
file_path: PaddleOCR/benchmark/PaddleOCR_DBNet/models/losses/basic_loss.py
imports: import paddle
  import paddle.nn
label_desc: Use image node_id 2 for calling the MaskL1Loss obj's underlying member method code with example usage: obj.forward(pred, gt, mask) and returns: loss