Learning To Simulate: unable to create animation

I was trying to recreate the 'learning to simulate example', and when I finished training the model and try to plot the trajectory using

`
python -m learning_to_simulate.render_rollout \
--rollout_path=/tmp/rollouts/WaterRamps/rollout_test_0.pkl
`

The error message was

`
Figure(1000x500)
/usr/local/lib/python3.7/site-packages/matplotlib/animation.py:888: UserWarning: Animation was deleted without rendering anything. This is most likely not intended. To prevent deletion, assign the Animation to a variable, e.g. `anim`, that exists until you have outputted the Animation using `plt.show()` or `anim.save()`.
`

What should I do to plot the animation?