Created by: TomorrowIsAnOtherDay

In save function, agent will save its learn_program if no program is provided. https://github.com/PaddlePaddle/PARL/blob/a50793e43acdbf5c27d5fd96bcec8b76dc777c0d/parl/core/fluid/agent.py#L154 What if the users haven't defined a program named learn_program?