Git error- fatal- Needed a single revision

Cloning/updating Appium sample-code submodule

Command failed
stdout:

stderr:
fatal: Needed a single revision
Unable to find current revision in submodule path ‘submodules/sample-code‘

Warning: Command failed: git submodule update --init "E:\project\appium\submodules\sample-code"
fatal: Needed a single revision
Unable to find current revision in submodule path ‘submodules/sample-code‘
Use --force to continue.

出现此问题的原因是 git更新太慢，中间中断过，解决办法，删掉sample-code文件夹或者里面的内容即可。