``getFieldValue`` does not exist.

If we want to avoid the double wrapping, I can remove the call to ``wrapJDIException`` in ``fieldValue``, since in the current codebase it's always accessed within a ``wrapJDIException``. Though, future code will have to remember this requirement. I don't think the double wrapping here will cause performance degradation, so I'd prefer to keep things as they are.