Null<std::string> and quote manipulator

[frank]

I need a nullable string type that can be inserted, properly escaped, 
into a mysqlpp::Query. I thought that Null<std::string> would be 
appropriate for this, but it doesn't quite work the way I expect it to. 
Specifically, when inserting a Null<std::string> into a Query using the 
quote manipulator, the string is not escaped. Is there a way to achieve 
what I'm looking for with mysqlpp that I am missing?

thanks,
frank