parsing XML gives me a list of slurpersupport attributes but I want a list of texts

I fetch an xml file from the internet using a URL

def url = "http://ift.tt/1pwoGOG".toURL()
InputStream inp = url.openStream()
def kursomgXML = new XmlSlurper().parse(inp).declareNamespace(xml:'http://ift.tt/1ikcaie')

I used the following :

courseRound.courseResponsibleList.courseResponsible.@primaryEmail.list()

which seemed to work fine but when using the result in a method call I get an error saying that no signature of the method is applicable on a value of type groovy.util.slurpersupport.Attribute

How do I get a list of strings instead of a list of slurpersupport attributes?