Constructor.newInstance() behaving differently in a JUnit vs actual runtime

I'm trying to use java.lang.reflect methods, in a RCP plug-in project to create a new instance of an object. If I use this:

constructorList[0].newInstance();

It works fine during runtime, (Running through the RCP App), but the line of code fails in a JUnit with: java.lang.IllegalArgumentException: wrong number of arguments

If I use this instead:

constructorList[0].newInstance(((Object) null));

It works fine running the JUnit, but fails with during runtime with: java.lang.IllegalArgumentException: wrong number of arguments

The only difference seems to be the code running within a plug-in vs a standalone JUnit. Does anyone know if this would probably be the root cause? I'm not sure on how to setup my JUnit to run as a JUnit Plug-in, so I haven't been able to test it out.

The JavaDoc for the newInstance method:

...

If the number of formal parameters required by the underlying constructor * is 0, the supplied initargs array may be of length 0 or null.

@param initargs array of objects to be passed as arguments to * the constructor call; values of primitive types are wrapped in * a wrapper object of the appropriate type (e.g. a float * in a {@link java.lang.Float Float})

...