Nullable enums with an empty string fail to get generated

[czechboy0]

In #59, we added support for an empty string as a valid case in a string enum, however, we only tested it on enum schemas not marked as nullable.

Turns out, that when marked as nullable, OpenAPIKit parses the values slightly differently, and treats the empty string as a nil string instead. That nil value, when converted to OpenAPIKit's AnyCodable, gets turned into a Void.

Before we introduce a workaround in the generator, @mattpolzin is this intentional behavior, and if so, can you say more about it please?

[czechboy0]

To reproduce, we can just use:

type: string
nullable: true
enum:
  - foo
  - ""

The second enum value will be an empty string when the schema is not nullable, and Void when the schema is nullable.

[mattpolzin]

Unfortunately this is a known issue with Yams. jpsim/Yams#301

OpenAPIKit has special case decoding of nullable string enums because otherwise a null case gets read in as the string "null" instead of the value null, but it is unintentional that the empty string also gets read in as null.

There is a proposed fix for the issue against Yams and a fork with that fix under the CreateAPI project but no indication of whether the fix will be upstreamed.

[czechboy0]

Thanks for the find, @mattpolzin - I wonder if @jpsim can tell us more about the prioritization of landing that fix?

[czechboy0]

I suspect we'll need to check for this ourselves in the generator, it's not a big deal, just wanted to try to see if Yams could fix it, but I suspect that'd be a breaking change anyway, so might not be likely.