The cloverphp-plugin repository does not contain any information about the license the code is distributed under. This could potentially hinder contributions from some countries, including Germany, where a license needs to be declared explicitly.

I would suggest choosing an MIT License, same as Jenkins Core.

As far as I can see, as this is no license change but just a formal declaration, the approval of all contributors is not required - as they have agreed to publish their work without a license specified.

I will gladly prepare a Pull Request, but I would love to see all contributors (sogabe, Tong Quach and ndeloof) of this project to agree.