def model_fn_example(dataset_tensor, batch_size, evaluation):
    """
    Example of the signature of the function that creates the model used in the
    Trainer and Evaluator.
    :param tf.Tensor dataset_tensor: the tensor created from the dataset
    :param int batch_size: the batch size for the model, the same used in the dataset.
    :param bool evaluation: True if this model is for evaluation, False if it is for training.
    :return: returns the graph data, this is what session.run will execute during the training,
    for the test it will only execute the summary operator.
    """
    graph_data = None
    return graph_data