vframeArrayElement::fill_in iterates MonitorInfo. When is_scalar_replaced is true, meaning the MonitorInfo has a null owner(), it only sets a null object in the BasicObjectLock.
BasicObjectLock was pulled from the MonitorChunks array with no other specific initialization.

unpack_on_stack has always called src->lock()->move_to(src->obj(), top->lock()); without checking src->obj() for null.

This not as yet know to cause a problem (crash), but looks like an existing bug, in that dest->lock() can be uninitialized, and could cause problems later on in unpack_on_stack if move_to sees a "neutral" value and tries to inflate.