[Scala] Async helper does not account for optional bodies

[gmarz]

Description

RequestWriter is typed to the body parameter, but does not account for the case where a body is not required, and thus is of type Option[T].

For instance:

def someOperation(body: SomeBody)(implicit reader: ClientResponseReader[SomeResponse], writer: RequestWriter[SomeBody)

is fine, but if if body above is Option[SomeBody] (because it's not required), then the following is generated:

def someOperation(body: Option[SomeBody] = None)(implicit reader: ClientResponseReader[SomeResponse], writer: RequestWriter[SomeBody)

which causes an error at this line because writer.write() is expecting SomeBody when it's actually Option[SomeBody].

Swagger-codegen version

2.3.0

Swagger declaration file content or url

https://download.elasticsearch.org/cloud/1.1/elastic-cloud-enterprise-API-swagger.json

Command line used for generation

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate \
  -i https://download.elasticsearch.org/cloud/1.1/elastic-cloud-enterprise-API-swagger.json \
  -l scala