DERBY-5111 NullPointerException on unique constraint violation with unique index

backported change #1579766 and #1582819 from trunk to 10.10 branch.  Some
manual changes and merging was necessary.

Patch derby-5111 and
Patch derby-5111-test, which adds the repro for this issue as a new test case.



git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/branches/10.10@1630239 13f79535-47bb-0310-9956-ffa450edef68