Checks the validity of the given value for the entry. This method does
basic checks such as null ness & type.
if (obj == null)
{
throw new InvalidConfigException(
strMgr.getString("validator.invalid_value", getName(), null));
}
Class c = obj.getClass();
if (!type.isAssignableFrom(c))
{
throw new InvalidConfigException(
strMgr.getString("validator.invalid_type",
getName(), type.getName(), c.getName()));
}