I'm trying to replace my use of `std.json` with `asdf`.
I ran into an issue where some JSON I throw at it has fields that
are sometimes null and sometimes not. I don't know how to tell
asdf not to throw when deserialising it.
Minimal example:
```d
{
"inner": {
"s": "foo"
}
}
```
This is the usual case, but sometimes the response is this.
```d
{
"inner": null
}
```
asdf behaves like so:
```d
/+dub.sdl:
dependency "asdf" version="~>0.7.17"
+/
import asdf;
struct S
{
static struct Inner
{
string s = "foo";
}
Inner inner;
}
void main()
{
S foo;
const good = foo.serializeToJson;
assert(good == `{"inner":{"s":"foo"}}`);
enum bad = `{"inner":null}`;
auto bar = bad.deserialize!S;
}
/*
mir.serde.SerdeException@.dub/packages/asdf/0.7.17/asdf/source/asdf/serialization.d(338):
Cann't deserialize Inner. Unexpected data: null_
*/
```
`asdf` has some UDAs that you can use to declare members and
fields as optional, which works well when fields are omitted, but
there doesn't seem to be something for when they're *there* but
unexpectedly null. There is a `@serdeTransformIn` that I had
hoped could maybe work to treat null as `Inner.init`, but the
docs were lacking and I couldn't get it to work.
What should I do? I don't want to just catch the exception but so
far that's the best solution I have.
