examples/DRL/main_reachable_domain.py not running

[bardhh]

I get the following error when running this script:
Traceback (most recent call last):
File "/usr/local/lib/python3.7/multiprocessing/process.py", line 297, in _bootstrap
self.run()
File "/usr/local/lib/python3.7/multiprocessing/process.py", line 99, in run
self._target(*self._args, **self._kwargs)
File "/home/veritex/src/veritex/methods/worker.py", line 104, in main_func
self.state_spawn_depth_first(tuple_state)
File "/home/veritex/src/veritex/methods/worker.py", line 364, in state_spawn_depth_first
self.state_spawn_depth_first(next_tuple_states[0])
File "/home/veritex/src/veritex/methods/worker.py", line 364, in state_spawn_depth_first
self.state_spawn_depth_first(next_tuple_states[0])
File "/home/veritex/src/veritex/methods/worker.py", line 364, in state_spawn_depth_first
self.state_spawn_depth_first(next_tuple_states[0])
[Previous line repeated 7 more times]
File "/home/veritex/src/veritex/methods/worker.py", line 358, in state_spawn_depth_first
self.collect_results(next_tuple_states[0][0])
File "/home/veritex/src/veritex/methods/worker.py", line 338, in collect_results
unsafe_inputs = self.dnn.backtrack(s) # in FVIM or Flattice
File "/home/veritex/src/veritex/networks/ffnn.py", line 164, in backtrack
for i in range(len(self.property.unsafe_domains)):
AttributeError: 'NoneType' object has no attribute 'unsafe_domains'