Gradle now uses separate output directories for each JVM language, but this build assumes a single directory for all classes from a source set. This behaviour has been deprecated and is scheduled to be removed in Gradle 5.0
at org.gradle.api.internal.tasks.DefaultSourceSetOutput.getClassesDir(DefaultSourceSetOutput.java:79)
at org.gradle.api.internal.tasks.DefaultSourceSetOutput_Decorated.getClassesDir(Unknown Source)
at me.tatarka.RetrolambdaPluginJava$_apply_closure1$_closure2.doCall(RetrolambdaPluginJava.groovy:43)
...
Gradle (4+) outputs the following warning: