[castor-user] Marshalling XML causes Cannot resolve a null or zero-length class name

[Toby]

Hi Folks,

Sorry if its a basic question but I can't get any clues as to why when
marshalling throws the following exception;

java.lang.IllegalArgumentException: Cannot resolve a null or zero-length
class name.
    at
org.exolab.castor.xml.util.XMLClassDescriptorResolverImpl.resolveByXMLName(XMLClassDescriptorResolverImpl.java:253)
    at org.exolab.castor.xml.Marshaller.marshal(Marshaller.java:1021)
    at org.exolab.castor.xml.Marshaller.marshal(Marshaller.java:1913)
    at org.exolab.castor.xml.Marshaller.marshal(Marshaller.java:838)
    at
com.racediary.io.BasicSerialisationTest.assertSerialisation(BasicSerialisationTest.java:115)
    at
com.racediary.io.BasicSerialisationTest.nonEmptyRaceCollectionSerialisation(BasicSerialisationTest.java:64)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

I kind of gather that the problem is that castor is trying to do something
with a class it sees as the empty string or null but I don't really see how?
I'm not using any mapping file here, just running a test which marshalls
then unmarshals an object.

Any clues as to what this error message actually means?

Thanks,
Toby