when test the grid scenario, there is an valueError - sumo

Question

On flow tutorial_8, I tried another scenario: SimpleGridScenario
I already check the grid.py, and followed the rules for the parameters.
My origianl program is that:
from flow.envs import Env
from gym.spaces.box import Box
from gym.spaces.tuple_space import Tuple
from flow.controllers import IDMController, ContinuousRouter,GridRouter
from flow.core.experiment import Experiment
from flow.core.params import SumoParams, EnvParams, \
InitialConfig, NetParams
from flow.core.params import VehicleParams
from flow.scenarios.loop import LoopScenario, ADDITIONAL_NET_PARAMS
from flow.scenarios.grid import SimpleGridScenario
from flow.scenarios import SimpleGridScenario
import numpy as np
from flow.envs import myEnv
ADDITIONAL_ENV_PARAMS={
"max_accel":1,
"max_decel":1,
}
sumo_params = SumoParams(sim_step=0.1,render=True)
vehicles=VehicleParams()
vehicles.add(
veh_id="idm",
acceleration_controller=(IDMController,{}),
routing_controller=(GridRouter,{}),
num_vehicles=22
)
env_params = EnvParams(additional_params=ADDITIONAL_ENV_PARAMS)
additional_net_params = ADDITIONAL_NET_PARAMS.copy()
net_params = NetParams(additional_params=additional_net_params)
initial_config = InitialConfig(bunching=20)
scenario = SimpleGridScenario(
name = 'grid',
vehicles = vehicles,
net_params = NetParams(
additional_params={
'grid_array':{
'row_num':3,
'col_num':2,
'inner_length':500,
'short_length':500,
'long_length':500,
'cars_top':20,
'cars_bot':20,
'cars_left':20,
'cars_right':20,
},
'horizontal_lanes':1,
'vertical_lanes':1,
'speed_limit':{
'vertical':35,
'horizontal':35
}
},
no_internal_links=False
),
initial_config = initial_config
)
env = myEnv(env_params, sumo_params, scenario)
exp = Experiment(env)
_ = exp.run(1, 1500)
And then I ran that, there is an error, the error log is：
(flow) dnl#dnl-Iiyama:~/flow$ python Tutorial_9_1.py
Loading configuration... done.
Success.
Loading configuration... done.
Error in edge length with key bot3_2
Error in edge length with key bot3_2
Traceback (most recent call last):
File "Tutorial_9_1.py", line 72, in <module>
_ = exp.run(1, 1500)
File "/home/dnl/flow/flow/core/experiment.py", line 118, in run
state = self.env.reset()
File "/home/dnl/flow/flow/envs/base_env.py", line 483, in reset
speed=speed)
File "/home/dnl/flow/flow/core/kernel/vehicle/traci.py", line 990, in add
[i for i in range(num_routes)], size=1, p=frac)[0])
File "mtrand.pyx", line 1126, in mtrand.RandomState.choice
ValueError: a must be non-empty
I want to why i am wrong ?
I try to test another scenario expect the LoopScenario. But it doesn't work
Please help.