POMDP Maze cannot be run in Pybrain

[semolnahali]

The following code is rl.py that implements mdp maze in pybrain:

from scipy import * #@UnusedWildImport
import matplotlib.pyplot as plt
from pybrain.rl.environments.mazes import Maze, MDPMazeTask
from pybrain.rl.learners.valuebased import ActionValueTable
from pybrain.rl.agents import LearningAgent
from pybrain.rl.learners import Q, SARSA #@UnusedImport
from pybrain.rl.experiments import Experiment

plt.gray()
plt.ion()
structure = array([[1, 1, 1, 1, 1, 1, 1, 1, 1],
[1, 0, 0, 1, 0, 0, 0, 0, 1],
[1, 0, 0, 1, 0, 0, 1, 0, 1],
[1, 0, 0, 1, 0, 0, 0, 0, 1],
[1, 0, 0, 1, 0, 1, 0, 0, 1],
[1, 0, 0, 0, 0, 0, 0, 0, 1],
[1, 0, 0, 0, 0, 0, 0, 0, 1],
[1, 0, 0, 0, 0, 0, 0, 0, 1],
[1, 1, 1, 1, 1, 1, 1, 1, 1]])
environment = Maze(structure, (7, 7))
controller = ActionValueTable(81, 4)
learner = Q()
agent = LearningAgent(controller, learner)
task = MDPMazeTask(environment)
experiment = Experiment(task, agent)
while True:
experiment.doInteractions(100)
agent.learn()
agent.reset()
plt.pcolor(controller.params.reshape(81,4).max(1).reshape(9,9))
plt.show()
plt.pause(0.1)

I tried to change it to pomdp maze by replacing 'task = MDPMazeTask(environment)' with 'task = TrivialMaze()
'

but this encountered the following errors :
Traceback (most recent call last):
File "/home/web/pybrain-master/docs/tutorials/rl.py", line 140, in
experiment.doInteractions(100)# speed of learning
File "/home/web/pybrain-master/pybrain/rl/experiments/experiment.py", line 18, in doInteractions
self._oneInteraction()
File "/home/web/pybrain-master/pybrain/rl/experiments/experiment.py", line 27, in _oneInteraction
self.task.performAction(self.agent.getAction())
File "/home/web/pybrain-master/pybrain/rl/agents/learning.py", line 50, in getAction
self.lastaction = self.module.activate(self.lastobs)
File "/home/web/pybrain-master/pybrain/structure/modules/module.py", line 121, in activate
assert len(self.inputbuffer[self.offset]) == len(inpt), str((len(self.inputbuffer[self.offset]), len(inpt)))
AssertionError: (1, 4)

Can anyone help me please?