apt-get An error occurred during the signature verification

When running apt update, i get following error

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://packages.cloud.google.com cloud-sdk-jessie InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6A030B21BA07F4FB

To fix this error, run

apt-key adv --keyserver keys.gnupg.net --recv-keys 6A030B21BA07F4FB