[kotlin][retrofit2]fix query parameter nullable #5859

[RyuNen344]

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project beforehand.
• Run the shell script ./bin/generate-samples.shto update all Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/config/java*.
• File the PR against the correct branch: master, 4.3.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

summary

fix Kotlin-client with retrofit2 doesn't generate nullable parameters

description

when parameter is not rquired, kotlin class should be nullable
so, I add check

issue

fix #5859

[auto-labeler]

👍 Thanks for opening this issue!
🏷 I have applied any labels matching special text in your issue.

The team will review the labels and make any necessary changes.

[kuFEAR]

Hi, this pr look like duplicate of #6456

[RyuNen344]

Hi, this pr look like duplicate of #6456

yap, sorry
i will close