code: def test_forward_none_ch_gpu(self):
      with testing.assert_warns(DeprecationWarning):
          self.link.to_gpu()
      inputs = (
          [None] * len(self.c_prevs)
          + [None] * len(self.h_prevs)
          + [cuda.to_gpu(self.x)]
      )
      self.check_forward_valid_none(*inputs)
  
imports: import unittest
  import numpy
  import chainer
  from chainer import backend
  from chainer.backends import cuda
  from chainer import gradient_check
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
label_desc: Use image node_id 8 for calling the TestTreeLSTM obj's underlying member method code with example usage: obj.test_forward_none_ch_gpu() without return types