[dart-dio-next] Improve handling nullable objects

[ahmednfwela]

Currently nullable types need to be handled better at serialization level, for example:
deserializing BuiltMap<String,JsonObject> when one of the values is null will throw an error at run time, since JsonObject is not a nullable type

these changes are not perfect, especially changing these

typeMapping.put("object", "JsonObject?");
typeMapping.put("AnyType", "JsonObject?");

imports.put("JsonObject?", "package:built_value/json_object.dart");

but I am not sure what's the best approach for putting the null operator (?) after a type ?

also this PR makes use of the FullType.nullable named constructor for defining serializers

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CC: @jaumard @josh-burton @amondnet @sbu-WBT @kuhnroyal @agilob

[kuhnroyal]

Not everything is nullable, we need to default to non-nullable.
This requires built_value >= 8.1.0

Do you have a sample spec for collections with nullable content?

[kuhnroyal]

I created #10122 for built_value update

[kuhnroyal]

Looking at Kotlin and C# implementations, none of them support null in collections. There also doesn't seem to be a representation for this in the specification.

Maybe a ref with nullable: true not sure.
I don't think we should merge this atm.

[ahmednfwela]

@kuhnroyal but there is a spec for this

• yaml: https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/test/resources/3_0/petstore-with-fake-endpoints-models-for-testing.yaml#L1822
• generated:
  

  openapi-generator/samples/openapi3/client/petstore/dart-dio-next/petstore_client_lib_fake/lib/src/model/nullable_class.dart

  Line 196 in cd4e7ad

  case r'array_nullable_prop':

[ahmednfwela]

The only problem I am facing is:
how to use JsonObject for non-nullable objects, and JsonObject? for nullable objects

[kuhnroyal]

I see, I didn't know that items can have nullable property.
You can try accessing this via CodegenProperty.items.isNullable or CodegenProperty.mostInnerItems.isNullable in the template. I don't think you need to change anything in the Java code. We definitely don't want JsonObject? in the type or import mapping.

[ahmednfwela]

@kuhnroyal what do you think about this change? I even removed the java code for the serializer type and wrote it in mustache using recursive patterns

[ahmednfwela]

also @wing328 can this be included in 5.2.1 ?

[kuhnroyal]

I like it but there is still a couple things open. I don't think this should go into 5.2.1

[ahmednfwela]

@kuhnroyal is there anything else I can fix on my end?

[kuhnroyal]

Really like what you did here! 2 small changes requested

[kuhnroyal]

Awesome work, that will also make it easier to fix a couple problems around missing serializers. Thanks!

[kuhnroyal]

@agilob Do you have anything else here?

[agilob]

LGTM

[kuhnroyal]

@wing328 This can be merged