Be advised that as of January 17, 2018 Kotlin 1.2.20 has been released.
However there appears to be at least one known bug/problem with Kotlin 1.2.20 when used with Spring which you can read about here
https://blog.jetbrains.com/kotlin/2018/01/kotlin-1-2-20-is-out/ if you search for these two entries:
Osahner says:
January 18, 2018 at 2:02 pm
...
larmic says:
January 18, 2018 at 8:02 pm
...
I'm certain that the Kotlin and/or Spring development teams are working to correct these issues as they have already been reported as noted in this post.
However they may be other issues which have not been reported yet (January 18, 2018).
If you revert back to Kotlin 1.2.10 you will not experience these bugs.
Just thought
you should know,
Pete