Generic types get mixed up

import groovy.transform.CompileStatic
import java.util.function.Function

@CompileStatic
class Test<R extends Integer> {
  def <V> V method(Function<Test, V> f) {
    /**
     * org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object '' with class 'java.lang.String' to class 'java.lang.Integer'
     * 	at Test.traverseFindResult(ConsoleScript4:7)
     * 	at Test$traverseFindResult.call(Unknown Source)
     * 	at ConsoleScript4.run(ConsoleScript4:12)
     */
    def v = f.apply(this) // V v = f.apply(this) doesn't work as well, but directly returning without assignment works
    return v
  }
}

new Test().method(new Function<Test, String>() {
  @Override
  String apply(Test test) {
    ""
  }
})