hg: jdk-updates/jdk12u: 8221924: get(null) on single-entry unmodifiable Map returns null instead of throwing NPE

[stuart.marks at oracle.com]

Changeset: 06591b07ba24
Author:    smarks
Date:      2019-04-09 09:49 -0700
URL:       http://hg.openjdk.java.net/jdk-updates/jdk12u/rev/06591b07ba24

8221924: get(null) on single-entry unmodifiable Map returns null instead of throwing NPE
Reviewed-by: redestad, lancea

! src/java.base/share/classes/java/util/ImmutableCollections.java
! test/jdk/java/util/Map/MapFactories.java