line 175, in print_outline elines =reasons_to_fail[0].traceback.splitlines() AttributeError: 'NoneType' object has no attribute 'traceback'

[flyingCloudRain]

when i run the demo watch it fails,the termail dont show the right
it remaind me like

Traceback (most recent call last):
File "e:\python27\lib\site-packages\lettuce\registry.py", line 15
ok
callback(_args, *_kw)
File "e:\python27\lib\site-packages\lettuce\plugins\colored_shell
line 175, in print_outline
elines =reasons_to_fail[0].traceback.splitlines()
AttributeError: 'NoneType' object has no attribute 'traceback'

Died with 'NoneType' object has no attribute 'traceback'
Traceback (most recent call last):
File "e:\python27\lib\site-packages\lettuce__init__.py", line 19
failfast=self.failfast))
File "e:\python27\lib\site-packages\lettuce\core.py", line 1237,
scenarios_ran.extend(scenario.run(ignore_case, failfast=failfas
File "e:\python27\lib\site-packages\lettuce\core.py", line 759, i
results.append(run_scenario(self, index, outline, run_callbacks
File "e:\python27\lib\site-packages\lettuce\core.py", line 740, i
o
reasons_to_fail)
File "e:\python27\lib\site-packages\lettuce\registry.py", line 15
ok
callback(_args, *_kw)
File "e:\python27\lib\site-packages\lettuce\plugins\colored_shell
line 175, in print_outline
elines =reasons_to_fail[0].traceback.splitlines()
AttributeError: 'NoneType' object has no attribute 'traceback'