import std.typecons;
struct Nested
{
float f;
}
struct T
{
string str;
Nullable!Nested nested;
}
T t;
assert(t.serializeToJson == `{"str":null,"nested":null}`);
t.str = "txt";
t.nested = Nested(123);
assert(t.serializeToJson == `{"str":"txt","nested":{"f":123.0}}`);
Nullable type serialization