DEV-9786 Make sure we don't flush nulls

git-svn-id: http://svn.terracotta.org/svn/ehcache@7701 b9324663-ca0f-0410-8574-be9b3887307d
DEV-9786 Merge r7701 from trunk

git-svn-id: http://svn.terracotta.org/svn/ehcache@7702 b9324663-ca0f-0410-8574-be9b3887307d
refactored

git-svn-id: http://svn.terracotta.org/svn/ehcache@7703 b9324663-ca0f-0410-8574-be9b3887307d