[Scala] Fix async helper methods when body is optional (#7274)

* [Scala] Fix async helper methods when body is optional

Closes #7272

* Update petstore sample

Author: gmarz

modules/swagger-codegen/src/main/resources/scala/api.mustache

@@ -95,7 +95,7 @@ class {{classname}}AsyncHelper(client: TransportClient, config: SwaggerConfig) e
 {{#operation}}
   def {{operationId}}({{#allParams}}{{^required}}{{paramName}}: Option[{{dataType}}] = {{#defaultValue}}Some({{defaultValue}}){{/defaultValue}}{{^defaultValue}}None{{/defaultValue}}{{#hasMore}},{{/hasMore}}
     {{/required}}{{#required}}{{paramName}}: {{dataType}}{{#defaultValue}} = {{{defaultValue}}}{{/defaultValue}}{{#hasMore}},
-    {{/hasMore}}{{/required}}{{/allParams}})(implicit reader: ClientResponseReader[{{#returnType}}{{returnType}}{{/returnType}}{{^returnType}}Unit{{/returnType}}]{{#bodyParams}}, writer: RequestWriter[{{dataType}}]{{/bodyParams}}){{#returnType}}: Future[{{returnType}}]{{/returnType}}{{^returnType}}: Future[Unit]{{/returnType}} = {
+    {{/hasMore}}{{/required}}{{/allParams}})(implicit reader: ClientResponseReader[{{#returnType}}{{returnType}}{{/returnType}}{{^returnType}}Unit{{/returnType}}]{{#bodyParams}}, writer: RequestWriter[{{^required}}Option[{{dataType}}]{{/required}}{{#required}}{{dataType}}{{/required}}]{{/bodyParams}}){{#returnType}}: Future[{{returnType}}]{{/returnType}}{{^returnType}}: Future[Unit]{{/returnType}} = {
     // create path and map variables
     val path = (addFmt("{{path}}"){{#pathParams}}
       replaceAll("\\{" + "{{baseName}}" + "\\}", {{paramName}}.toString){{/pathParams}})