树莓派apt-get The value '\stable' is invalid for APT 错误

对apt-get进行任何操作都会报错：

pi@raspberrypi:~ $ sudo apt-get upgrade

Reading package lists... Done

E: The value '\stable' is invalid for APT::Default-Release as such a release is not available in the sources

解决方法：把/etc/apt/apt.conf.d/10defaultRelease这个文件删了。