message: Add the docstring for tf.keras.optimizers.serialize()
diff: @@ -43,6 +43,22 @@ from tensorflow.python.util.tf_export import keras_export
  @keras_export('keras.optimizers.serialize')
  def serialize(optimizer):
  + """Serialize the optimizer configuration to JSON compatible python dict.
  +
  + The configuration can be used for persistence and reconstruct the `Optimizer`
  + instance again.
  +
  + >>> tf.keras.optimizers.serialize(tf.keras.optimizers.SGD())
  + {'class_name': 'SGD', 'config': {'name': 'SGD', 'learning_rate': 0.01,
  + 'decay': 0.0, 'momentum': 0.0,
  + 'nesterov': False}}
  +
  + Args:
  + optimizer: An `Optimizer` instance to serialize.
  +
  + Returns:
  + Python dict which contains the configuration of the input optimizer.
  + """
  return serialize_keras_object(optimizer)
  