additionalProperties property
If type is OBJECT, specifies how to handle properties not defined in
properties.
If it is a boolean false, no additional properties are allowed. If it is
a schema, additional properties are allowed if they conform to the schema.
Optional.
The values for Object must be JSON objects. It can consist of num,
String, bool and null as well as Map and List values.
Implementation
core.Object? additionalProperties;