Charset cannot be null

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1603965 13f79535-47bb-0310-9956-ffa450edef68
CSV-117 Validate format parameters in constructor

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/csv/trunk@1603967 13f79535-47bb-0310-9956-ffa450edef68