NullPointerException in syncronized(){} block

Question

I have some code that produces, once in a great while, a NullPointerException when exiting a synchronized block (the debugger says that the line generating the exception is the block closing brace). I am wondering if there is any legitimate way that exiting such a block can throw a NullPointerException or if I should try to make a reproducible test case to report as a bug. This is on 1.4.0_01. The incidence of these NPEs is greatly increased when the profiler is in use, but they still occur even without it. Although in my current application the method is called from native code, the method in question does not use any native resources itself.
Any information on the subject would be appreciated. Thank you.

Answer 1

I could imagine that the following case gives you a
NullPointerException as you describe:
Object lock = new Object();
synchronized(lock) {
// ... some code here
lock = null;
} // NullPointerException is thrown hereJust to
give you an idea.
PierreThat would be a huge error. An aquired lock should create a copy of an instance (just like a parameter in a functioncall) or at least increase the reference count of the object.