[WFLY-3978] - PicketLink EAP 6.4 Issues

...der element.
I still don't think this can ever happen since security-domain is not nillable. Last night when we talked you were experimenting with 

     /.../identity-provider=xxxx:undefine-attribute(name=security-domain)

that one is nillable. The test you need to try is 

     /.../security-provider=xxxx:undefine-attribute(name=security-domain)

and the standard validators should pick that up in the call to

    attributeDefinition.validateAndSet(syntheticOp, submodel);

in AbstractWriteAttributeHandler. So, I don't think this validator is necessary.