docstr: Test flattening with zero sizes.
code: def test_flatten_batch_to_2d_zero_sizes(self):
      """Test flattening with zero sizes."""
      data = np.ones(shape=(10, 5, 3, 2))
      sizes = np.zeros(shape=(10, 5), dtype=np.int32)
  
      y, unflatten = utils.flatten_batch_to_2d(data, sizes)
  
      self.assertAllEqual([0, 2], tf.shape(input=y))
      self.assertAllEqual(np.zeros_like(data), unflatten(y))
  
imports: from absl.testing import parameterized
  import numpy
  from scipy import linalg
  import tensorflow
  from tensorflow_graphics.geometry.convolution import utils
  from tensorflow_graphics.util import test_case
label_desc: Use image node_id 6 for calling the UtilsFlattenBatchTo2dTests obj's underlying member method code with example usage: obj.test_flatten_batch_to_2d_zero_sizes() without return types