code: def testGradientTapeNoneGradients(self):
      y = np.asarray(2.0)
  
      with tf.GradientTape() as t:
          x = np.asarray(3.0)
          t.watch([x])
          z = 2 * x
  
      dz = t.gradient(z, y)
  
      self.assertIsNone(dz)
  
imports: import numpy
  import tensorflow.compat.v2
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops.numpy_ops import np_math_ops
label_desc: Use image node_id 3 for calling the InteropTest obj's underlying member method code with example usage: obj.testGradientTapeNoneGradients() without return types