TypeError: 'NoneType' object is not subscriptable

[liuliangxin]

Traceback (most recent call last):
File "D:\Python Project\phantom\network_simulation\run_simulation.py", line 118, in
run_simulation()
File "D:\Python Project\phantom\network_simulation\run_simulation.py", line 92, in run_simulation
simulation = Simulation(honest_hash_rates=honest_hash_rates,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "D:\Python Project\phantom\network_simulation\simulation.py", line 150, in init
self._network = Network(self._propagation_delay_parameter, self._median_speed,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "D:\Python Project\phantom\network_simulation\network.py", line 47, in init
self._total_network_dag.add(self._GENESIS_BLOCK)
File "D:\Python Project\phantom\phantom\phantom.py", line 103, in add
self._G.node[global_id][self._BLOCK_DATA_KEY] = block
~~~~~~~~~~~~^^^^^^^^^^^
TypeError: 'NoneType' object is not subscriptable