RFR(L): 8218628: Add detailed message to NullPointerException describing what is null.

[Mandy Chung]

Hi Goetz,

Roger, Coleen, Maurizio and I talked about this proposed feature.
We all think that improving NPE message is a useful enhancement for
the platform and helps developers to tell what causes NPE.

This is not a small enhancement.  Diving into a large code review
would not be the best way to move this forward as you can see the
discussion so far.

It would help if you can start with writing down the problem and
the proposal like what improvements are proposed and under what
circumstances may be acceptable that NPE message won't be improved.
This would get the discussion on the proposal feature and then
the discussion of the best way to to implement it in the VM, library,
or combination.  You can consider using the JEP template that gives
you a good structure to follow for the write up.

What do you think?

Mandy