Hello, @NorseDreki.
Regarding the exception:
Execution failed for task ':sonar'. class java.lang.String cannot be cast to class java.util.Collection (java.lang.String and java.util.Collection are in module java.base of loader 'bootstrap')
It has been fixed by SCANGRADLE-133, and it is available in the Scanner for Gradle version 5.0.0.4637.
To help you the best, could you share your analysis configuration and the command you run to trigger the analysis?
The Kotlin analyzer relies on the Jetbrains Kotlin Compiler libraries, so the AST and the Semantics are provided to us.
Cheers,
Angelo