Escaped semicolon + sprintf weirdness

I encountered a strange bug in my patch tonight and I'm trying to understand what Max/mxj is doing.

I had a message with an escaped semicolon, like 'a;b'. It went through an [sprintf] object before getting sent to an [mxj] external. Then in my anything(String msg, Atom[] args) method, one of the args was null and I got a NullPointerException.

I also see a strange error in the Max window:
newAtom: default (10)

After some debugging I determined that the semicolon character came through as an Atom in the args array, but it was represented by a null.

I fixed my patch by using a [sprintf symout ...] but I'd like to make my mxj objects as robust as possible.

If anyone can enlighten me as to what's going on here I'd appreciate it. Is it safe to assume that whenever anything() receives a null argument, that it represents the semicolon character? Is it possible this is a bug in [mxj]?

Here's some Java code and a patch to demonstrate. When clicking on the right message box, the Max window shows:

newAtom: default (10)
Message 'a' with 2 args:
null
'b'

--------

import com.cycling74.max.Atom;
import com.cycling74.max.MaxObject;

public class wheresMySemicolon extends MaxObject {

    public void anything(String msg, Atom[] args) {
        System.out.println("Message '" + msg + "' with " + args.length + " args:");
        for (Atom arg : args) {
            if (arg == null) {
                System.out.println(" null");
            }
            else if (arg.isString()) {
                System.out.println(" '" + arg + "'");
            }
            else {
                System.out.println(" " + arg);
            }
        }
    }
}