avoid NullPointerExceptions if Date is null

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1529672 13f79535-47bb-0310-9956-ffa450edef68
backwards incompatible changes

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/compress/trunk@1529673 13f79535-47bb-0310-9956-ffa450edef68