linux mint Serena package problem.

[RecNes]

@JonasGroeger

W: The repository 'https://packagecloud.io/JonasGroeger/soundnode/linuxmint serena Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

I think this information is enough to explain the problem. Please contact with me if you have any further questions.