SpringBoot kotlin-maven-plugin doesn't accept java.version 8 as jvmTarget

https://github.com/spring-projects/spring-boot/blob/2b94484078f6ed3f1d373e8146efaaecddcd9964/spring-boot-project/spring-boot-starters/spring-boot-starter-parent/build.gradle#L59

The maven compiler plugin and plexus compiler are ambiguous to the formatting of the java version before java 9 (e.g. 1.8 vs 8). Unfortunately this is not the case for the jetbrains kotlin-maven-plugin. And results in an error when 8 is used instead of 1.8. I wasn't able to find any documentation on the java.version property so it is unclear to me if this is expected/known behaviour.

Comment From: wilkinsona

This is to be expected. java.version defaults to 1.8 in the pom for 2.7.x where that is our baseline version of Java so that it's compatible with all plugins on which it's configured.