code: def forward(self, x, rel_pos_bias=None):
      if self.gamma_1 is None:
          x = x + self.drop_path(
              self.attn(self.norm1(x), rel_pos_bias=rel_pos_bias)
          )
          x = x + self.drop_path(self.mlp(self.norm2(x)))
      else:
          x = x + self.drop_path(
              self.gamma_1
              * self.attn(self.norm1(x), rel_pos_bias=rel_pos_bias)
          )
          x = x + self.drop_path(self.gamma_2 * self.mlp(self.norm2(x)))
      return x
  
imports: import os
  import math
  import numpy
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle.nn.initializer import TruncatedNormal, Constant, Normal
  from paddleseg.cvlibs import manager
  from paddleseg.utils import utils, logger
  from paddleseg.models.backbones.transformer_utils import to_2tuple, DropPath, Identity
label_desc: Use image node_id 2 for calling the Block obj's underlying member method code with example usage: obj.forward(x, rel_pos_bias) and returns: x