RFR: JDK-8204172 Predicate::not should explicitly mention "NullPointerException - if target is null"

[Jim Laskey]

CSR: https://bugs.openjdk.java.net/browse/JDK-8204959
webrev: http://cr.openjdk.java.net/~jlaskey/8204172/webrev/index.html

Thank you,

— Jim