AttributeError: 'NoneType' object has no attribute 'strip' ?

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Hello ! I am trying to install asctec_drivers so that I can control the quadrotor through ros in morse simulator.

When I try to run the rosdep install asctec_drivers i get the following error

ERROR: Rosdep experienced an error: 'NoneType' object has no attribute 'strip' Please go to the rosdep page [1] and file a bug report with the stack trace below. [1] : 
rosdep version: 0.10.27

Traceback (most recent call last):   File "/usr/local/lib/python2.7/dist-packages/rosdep2/main.py", line 121, in rosdep_main
    exit_code = _rosdep_main(args)   File "/usr/local/lib/python2.7/dist-packages/rosdep2/main.py", line 279, in _rosdep_main
    return _package_args_handler(command, parser, options, args)   File "/usr/local/lib/python2.7/dist-packages/rosdep2/main.py", line 335, in _package_args_handler
    val = rospkg.expand_to_packages(args, rospack, rosstack)   File "/usr/local/lib/python2.7/dist-packages/rospkg/rospack.py", line 419, in expand_to_packages
    package_list = rospack.list()   File "/usr/local/lib/python2.7/dist-packages/rospkg/rospack.py", line 179, in list
    self._update_location_cache()   File "/usr/local/lib/python2.7/dist-packages/rospkg/rospack.py", line 171, in _update_location_cache
    list_by_path(self._manifest_name, path, cache)   File "/usr/local/lib/python2.7/dist-packages/rospkg/rospack.py", line 68, in list_by_path
    resource_name = root.findtext('name').strip(' \n\r\t') AttributeError: 'NoneType' object has no attribute 'strip'

I would really appreciate if anybody can tell me how to overcome this error Thanks