Error updating Linux-sdk for Face-RK3399

[raibopavan]

while doing "repo sync -c" for Face-RK3399

~/linux/linux-sdk$ ../repo/repo sync -c
Fetching project rk_pcba_test
Fetching project powermanager
Fetching project camera
Fetching project rkbin
Fetching project device-custom
Fetching project music
Fetching project tools
Fetching project audioservice
Fetching project demo
Fetching project linux-rga
Fetching project libdrm-rockchip
Fetching project buildroot
Fetching project docs
Fetching project rkupdate
Fetching project mpv
Fetching project rkssd
Fetching project alsa-config
Fetching project gcc-linaro-6.3.1-2017.05-x86_64_aarch64-linux-gnu
Fetching project recovery
Fetching project bluez-alsa
Fetching project u-boot
Fetching project video
Fetching project camera_engine_cifisp
Fetching project rk-rootfs-build
Fetching project gst-plugins-rockchip
Fetching project gallery
Fetching project mpp
Fetching project tensorflow
Fetching project gstreamer-camera
Fetching project libmali
Fetching project rkwifibt
Fetching project QLauncher
Fetching project ffmpeg
Fetching project rkscript
Fetching project settings
Fetching project kernel
Fetching project gstreamer-rockchip
Fetching project camera_engine_rkisp
Fetching project distro
Fetching project dl
error: Cannot fetch kernel (GitError: kernel update-ref: fatal: a179e62^0: not a valid SHA1
)
Exception in thread Thread-36:
Traceback (most recent call last):
File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
self.run()
File "/usr/lib/python2.7/threading.py", line 754, in run
self.__target(*self.__args, **self.__kwargs)
File "/home/sravan/linux/repo/subcmds/sync.py", line 270, in _FetchProjectList
success = self._FetchHelper(opt, project, *args, **kwargs)
File "/home/sravan/linux/repo/subcmds/sync.py", line 314, in _FetchHelper
prune=opt.prune)
File "/home/sravan/linux/repo/project.py", line 1271, in Sync_NetworkHalf
self._InitMRef()
File "/home/sravan/linux/repo/project.py", line 2364, in _InitMRef
self._InitAnyMRef(R_M + self.manifest.branch)
File "/home/sravan/linux/repo/project.py", line 2376, in _InitAnyMRef
self.bare_git.UpdateRef(ref, dst, message=msg, detach=True)
File "/home/sravan/linux/repo/project.py", line 2673, in UpdateRef
self.update_ref(*cmdv)
File "/home/sravan/linux/repo/project.py", line 2747, in runner
(self._project.name, name, p.stderr))
GitError: kernel update-ref: fatal: a179e62^0: not a valid SHA1

error: Exited sync due to fetch errors