Java interfaces generated by javamaker doesn't seem to use the @NonNull annotation for out parameters.
When calling such a method with a null argument where an out parameter is expected, the java uno bridge will terminate with an exception triggered by the following code in urp.java (because args[i] == null).

         if (argTypes != null) {
             for (int i = 0; i < argTypes.length; ++i) {
                 if (argTypes[i] != null) {
                     Array.set(
                         args[i], 0,
                         unmarshal.readValue(
                             argTypes[i].getComponentType()));

When adding @NonNull to such out arguments, java would prevent the caller to accidentally pass null.

To make this method more safe, I'd suggest to also add a try/catch around the Array.set(...) call, which would return an exception to the caller.