Changing MBeanSkeleton per the following diff resolved the problem:
diff --git a/src/main/java/org/glassfish/gmbal/impl/MBeanSkeleton.java
b/src/main/java/org/glassfish/gmbal/impl/MBeanSkeleton.java
--- a/src/main/java/org/glassfish/gmbal/impl/MBeanSkeleton.java
+++ b/src/main/java/org/glassfish/gmbal/impl/MBeanSkeleton.java
@@ -643,7 +643,7 @@
String sig[]) throws MBeanException, ReflectionException {
final List<String> signature = Arrays.asList(sig);
- final List<Object> parameters = Arrays.asList(params);
+ final List<Object> parameters = (params == null) ?
Arrays.asList() : Arrays.asList(params);
final Map<List<String>, Operation> opMap = operations.get(
actionName);