JDK-8196298: Add null Reader and Writer

[Alan Bateman]

On 29/01/2018 22:55, Brian Burkhalter wrote:
> I made a few minor changes to the CSR [1] verbiage. Probably the nullWriter() documentation should also be updated to explicitly mention all variants of both append() and write().
>
It could although limiting it to the abstract methods should be fine too 
as the append methods are specified in terms of the write methods.

One other micro detail is that Reader/Writer support implementations 
specifying the object to use for synchronization. This isn't interesting 
for the Reader/Writer objects returned by the proposed static methods so 
a one-line that says that the object used to synchronize operations is 
not specified might help. It would avoid something synchronizing on the 
reader or writer and expecting operations read/write methods to block.

-Alan