各位大神有遇到过下载android源码出现的如下错误吗？：
error: Cannot fetch repo (TypeError: unsupported operand type(s) for +: 'NoneType' and 'str')
Fetching project platform/libcore
Exception in thread Thread-242:
Traceback (most recent call last):
File "/usr/lib/python2.7/threading.py", line 551, in bootstrap_inner
self.run()
File "/usr/lib/python2.7/threading.py", line 504, in run
self.target(*self.__args, **self.__kwargs)
File "/home/liubaoli/android/.repo/repo/subcmds/sync.py", line 273, in _FetchProjectList
success = self._FetchHelper(opt, project, *args, **kwargs)
File "/home/liubaoli/android/.repo/repo/subcmds/sync.py", line 317, in _FetchHelper
prune=opt.prune)
File "/home/liubaoli/android/.repo/repo/project.py", line 1255, in Sync_NetworkHalf
and self._ApplyCloneBundle(initial=is_new, quiet=quiet):
File "/home/liubaoli/android/.repo/repo/project.py", line 2091, in _ApplyCloneBundle
bundle_url = remote.url + '/clone.bundle'
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'
Fetching projects: 58% (240/413) ^Cerror: Cannot fetch platform/libcore
error: Cannot fetch platform/external/iproute2
我用的是清华的镜像，下载android4.4.4_r1源码，下载了几次，都是卡在这里。目前已经下载了45个G，我是写了脚本让它自动下载的，但是总是会卡在这不动了。麻烦高手解答，感激不尽。
