Fixes #3055

fixes Spurious failure oientExecutionPoolSizeLowTest
Fixed checkstyle issues
fix null oldvalue in update events within transaction. fixes #3406
test cleanup
Merge pull request #3419 from eminn/fix/txn-map-update-event-null-oldvalue

fix null oldvalue in update events within transaction. fixes #3406
documentation update for issue #3428 (throws exception in case of non-comparable)
Merge pull request #3435 from serkan-ozal/fix/master/issue-3428

documentation update for issue #3428 on master branch
Merge pull request #3423 from pveentjer/fix/3.x/3055-clientexecutionpoolsizelowtest

Fixes #3055
Merge remote-tracking branch 'origin/master' into fix/master/issue-3047
checkstyle fix for issue #3047