RFR: [8039396] NPE when writing a class descriptor object to a custom ObjectOutputStream

[Ivan Gerasimov]

Hello everybody!

ObjectStreamClass#forClass() function is allowed to return null, if the 
local VM does not have the corresponding local class.
Because of that, NPE can be encountered during serialization through a 
subclass of ObjectOutputStream.

Would you please help review the fix?

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8039396
WEBREV: http://cr.openjdk.java.net/~igerasim/8039396/0/webrev/

Sincerely yours,
Ivan