Fix setup for empty list of classes

Author: marcphilipp

platform-tooling-support-tests/projects/graalvm-starter/build.gradle.kts

@@ -40,7 +40,10 @@ graalvmNative {
 binaries {
 named("test") {
 buildArgs.add("-H:+ReportExceptionStackTraces")
-buildArgs.add("--initialize-at-build-time=${initializeAtBuildTime.values.flatten().joinToString(",")}")
+val classNames = initializeAtBuildTime.values.flatten()
+if (classNames.isNotEmpty()) {
+buildArgs.add("--initialize-at-build-time=${classNames.joinToString(",")}")
+}
 }
 }
 }