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

[Langer, Christoph]

Hi Goetz,

> ok, so here a new webrev just adding a setter for the field:
> http://cr.openjdk.java.net/~goetz/wr19/8218628-exMsg-NPE/02
> 
> ... and incorporating the other comments.

Looks better ��

I have a few additions to src/java.base/share/classes/java/lang/NullPointerException.java:

28 import java.lang.reflect.Field;
29
-> can be removed now.

91         synchronized (this) {
-> I think this is not needed here. The transient modifier for lazyComputeMessage already implies the lock on the Object, I think.

108         return extendedMessage;
-> I guess it would be more correct if you returned super.getMessage() here.

Thanks
Christoph