v0.20.0

• YAML: Emit null instead of an empty scalar for nulls. In 0.18.0 Remarshal switched to an empty scalar (meaning, foo: with no value after the key) to represent nulls. This was the result of migrating to the ruamel.yaml library, where it is the default. While both representations are valid YAML 1.2, people tend to write and expect null. The current release restores pre-0.18.0 behavior.