* Implement Message.__bool__ with similar semantics to a collection, such that any value being set on the message (i.e. having a non-default value) make the Message value truthy .
Co-authored-by: nat <n@natn.me>
- replace some usages of `==` with `is`
- use available constants instead of magic strings for type names
Co-authored-by: nat <nat.noordanus@gmail.com>