vibe.d Serialize/Deserialize SumType to/from json

[Antonio]

D offers `SumType` struct to manage tagged Union types.

But there is no support for managing it's Json 
serialization/deserialization (using vibe.d)

Is it a way to add `fromRepresentation` and `toRepresentation` to 
`SumType` (or a way for creating a custom struct "inheriting" 
SumType with serialization capabilities)?

Thank you for advanced.