[BUG][Kotlin] Default value should be generated in query param using Retrofit2

Created by: alitams

Bug Report Checklist

Have you provided a full/minimal spec to reproduce the issue?
Have you validated the input using an OpenAPI validator (example)?
Have you tested with the latest master to confirm the issue still exists?
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Description

If the path has a query parameter which has default value, then the default value is not generated.

Generated output:

@POST("foo/bar")
fun inbox(@Query("size") size: kotlin.Int? = null): Completable

Expected output:

@POST("foo/bar")
fun inbox(@Query("size") size: kotlin.Int? = 10): Completable

openapi-generator version

5.3.0

OpenAPI declaration file content or url

  /foo/bar:
    post:
      tags:
        - "Foo"
      summary: "Retrieves something."
      description: "Provides something"
      operationId: "opid"
      parameters:
        - name: "size"
          in: "query"
          description: "Size"
          required: false
          schema:
            type: "integer"
            default: 10
    responses:
        "200":
          description: "Success."

Generation Details

Use the retrofit2 library.

Run this:

java -jar -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005 modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
   -i xyz.yaml \
   -g kotlin-client \
   -o gen/generated \
   --additional-properties=library=jvm-retrofit2,useRxJava3=true,dateLibrary=threetenbp-localdatetime,enumPropertyNaming=UPPERCASE,serializationLibrary=jackson,enablePostProcessFile=true

Steps to reproduce

Generate code with a path which has at least one parameter with a default value.

Related issues/PRs

In angular

Suggest a fix

In kotlin-client/libraries/jvm-retrofit2/queryParams.mustache Modify:

 {{^required}}? = null{{/required}}

part to:

{{#required}}{{#defaultValue}} = {{{.}}}{{/defaultValue}}{{/required}}{{^required}}?{{#defaultValue}} = {{{.}}}{{/defaultValue}}{{^defaultValue}} = null{{/defaultValue}}{{/required}}