char cannot be serialized as attribute

I would like to serialize 'char' field as xml attribute. I used the following (pseudo)code:

class A {
char x;
}
XStream xstr = new XStream();
xstr.useAttributeFor(A.class, "x");
System.out.println(xstr.toXML(new A()));

But no success. The workaround was to define my own Converter, with which it worked.
I expected that such a thing should be defined by default.

xstr.registerConverter(new SingleValueConverter(){
public Object fromString(String arg0)

{ return arg0.charAt(0); }

public String toString(Object arg0)

{ return String.valueOf(((Character)arg0)); }

public boolean canConvert(Class arg0)

{ return (Character.class.isAssignableFrom(arg0)); }

});