[BEANUTILS-458] Added a check for null result objects.

A null input object should be accepted by a converted without throwing a
ConversionException. Thanks to Manuel Dominguez Sarmiento for the proposed fix.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/beanutils/trunk@1597432 13f79535-47bb-0310-9956-ffa450edef68
[BEANUTILS-458] Updated changes.xml.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/beanutils/trunk@1597433 13f79535-47bb-0310-9956-ffa450edef68