message: Add empty-input test to unique_op_test.py
  This ensures the op works when operating on a zero-sized input tensor.
diff: @@ -152,6 +152,14 @@ class UniqueTest(test.TestCase):
  _, idx = gen_array_ops.unique_v2(x, axis=axis_t)
  self.assertEqual(idx.shape.as_list(), [None])
  + def testEmpty(self):
  + x = np.random.randint(2, size=0)
  + y, idx = array_ops.unique(x)
  + tf_y, tf_idx = self.evaluate([y, idx])
  +
  + self.assertEqual(len(x), len(tf_idx))
  + self.assertEqual(len(tf_y), len(np.unique(x)))
  +
  class UniqueWithCountsTest(test.TestCase):
  