code: def testNoneValuesCaught(self):
      observation = (1, 2)
      reward = (None, None)
      with self.assertRaises(ValueError):
          ts.transition(observation, reward)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import sys
  import numpy
  import tensorflow
  from tf_agents.specs import array_spec
  from tf_agents.specs import tensor_spec
  from tf_agents.trajectories import time_step
  from tf_agents.utils import nest_utils
label_desc: Use image node_id 13 for calling the TFTimeStepTest obj's underlying member method code with example usage: obj.testNoneValuesCaught() without return types