Optimize the code style

[TyrantLucifer]

Purpose of this pull request

Optimize the code style for plugin kv to make it more in line with functional programming

Check list

• Code changed are covered with tests, or it does not need tests for reason:
  It only changed the code of style, not effected the original function
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/incubator-seatunnel/tree/dev/docs

[CalvinKirs]

TBH, this change may not make much sense in my opinion.

[TyrantLucifer]

TBH, this change may not make much sense in my opinion.

Haha, it’s okay, I think it’s more elegant to write code like this in scala, if you don’t think it is necessary, you can turn off this pr, thank you for your reply😉

[garyelephant]

TBH, this change may not make much sense in my opinion.

agreed, and will close this. Thanks for your contribution @TyrantLucifer