RFR (S) 8073479: Replace obj.getClass hacks with Objects.requireNonNull

[Aleksey Shipilev]

Hi,

Please review and sponsor this cleanup fix:
  http://cr.openjdk.java.net/~shade/8073479/webrev.00/
  https://bugs.openjdk.java.net/browse/JDK-8073479

Summary: use Objects.requireNonNull instead of object.getClass to check
for nullity.

Testing:
  - jdk9-dev build on Linux x86_64/release
  - JPRT (modulo some freetype and javac failures)

Thank you,
-Aleksey.

P.S. I am going to submit another one against langtools, should it be
reviewed on this list as well?