TypeError: unsupported operand type(s) for -: 'int' and 'NoneType'

[fmalato]

I installed the environment as specified in the README.md file, using conda:

git clone https://github.com/iglu-contest/gridworld.git
cd gridworld && conda env create -f env.yml

Then I found out that gridworld doesn't get installed, so I installed it manually with cd gridworld && pip install -e .

Now when I try to run the example code, I get this error:

Traceback (most recent call last):
  File "main.py", line 17, in <module>
    obs, reward, done, info = env.step(action)
  File "/home/federima/miniconda3/envs/gridworld_env/lib/python3.7/site-packages/gym/wrappers/order_enforcing.py", line 13, in step
    observation, reward, done, info = self.env.step(action)
  File "/home/federima/PycharmProjects/gridworld_test/gridworld/gridworld/env.py", line 326, in step
    obs, reward, done, info = super().step(action)
  File "/home/federima/miniconda3/envs/gridworld_env/lib/python3.7/site-packages/gym/core.py", line 280, in step
    return self.env.step(action)
  File "/home/federima/PycharmProjects/gridworld_test/gridworld/gridworld/env.py", line 290, in step
    synthetic_grid = self.grid - self._synthetic_init_grid
TypeError: unsupported operand type(s) for -: 'int' and 'NoneType'