CSV-122: NullPointerException when empty header string and and null string of "". Thanks to Mike Lewis.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1609768 13f79535-47bb-0310-9956-ffa450edef68
Add CSV-122 to RELEASE-NOTES.txt

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1609769 13f79535-47bb-0310-9956-ffa450edef68