Gradle plugin fails with 'Unsupported javaVersion [13.]'

[igorbolic]

I'm using the Rocker Gradle plugin version 1.2.2 and JDK 13.

When I use the plugin with default configuration, and try to generate the templates, the build is failing with:

Execution failed for task ':generateRockerTemplateSource'.
Unsupported javaVersion [13.]

When I specify the Java version for the plugin:

rocker {
    javaVersion '13'
}

build runs successfully and the templates are generated.