>The dataset initially is created empty (as you could see from the code above). Then by reading the xml schema (from .xsd file) the dataset data types are defined. Then the XML is read into the dataset. So I don't see where a NULL value would get there.

This syntax should be accepted. I cannot see what is conflicting. Try 0 instead of false. That should also be supported. Or, if this is the default, maybe you do not need to put it.