I think this sentence contradicts itself.

A "license" implies that there is a copyright holder who allows usage of the work under the terms of said license.

While "Public domain" implies that there is no copyright holder (e.g. because the copyright expired, was explicitly waived, or is for some other reason not applicable).

If you want to put your work in the public domain, you can do so; simply include a note saying that you dedicate it to the public domain.