`sudo cpanm Types::Serialiser` only installs `Types::Serialiser` and `Types::Serialiser::Error`, and `sudo cpanm Types::Serialiser::Boolean` install all of the `Types::Serialiser` package. There is some oddity in that. The Ubuntu package only includes what you get with `sudo cpanm Types::Serialiser`.
This no longer works. The Types::Serialiser::Boolean package is no longer available on cpan.
My suggestion to add [qw(Types::Serialiser)] to the ${pg}{modules} list still works.