'Event' object has no attribute 'button'

[CrsiX]

I downloaded and started visgraph_simulator as mentioned in the README file.

After some experimenting with the UI and drawing some obstacles, I entered the S mode. I set the start point and then tried to move around with the end points by holding down the right mouse key. The "game" crashed almost instantly.
I retried this procedure with only two obstacles and by clicking instead of holding down the mouse. Same consequence.

Traceback:

pygame 1.9.5
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Traceback (most recent call last):
  File "visgraph_simulator/visgraph_simulator.py", line 237, in <module>
    game_loop()
  File "visgraph_simulator/visgraph_simulator.py", line 193, in game_loop
    if pygame.mouse.get_pressed()[LEFT-1] or event.button == LEFT:
AttributeError: 'Event' object has no attribute 'button'