当我执行sudo add-apt-repository -y ppa:ethereum/ethereum这会给我一个错误，比如，
gpg: keybox '/tmp/tmpy4v562r0/pubring.gpg' created gpg:
/tmp/tmpy4v562r0/trustdb.gpg: trustdb created gpg: key
1C52189C923F6CA9: public key "Launchpad PPA for Ethereum" imported
gpg: Total number processed: 1 gpg: imported: 1
**gpg: no valid OpenPGP data found.**
我尝试了很多方法来解决但没有运气。请帮我解决这个问题