check assertion for null

bwreg-service/src/main/java/edu/kit/scc/webreg/service/impl/UserUpdater.java

@@ -258,6 +258,7 @@ public class UserUpdater implements Serializable {
 	public SamlUserEntity updateUser(SamlUserEntity user, Assertion assertion, String executor, ServiceEntity service)
 			throws UserUpdateException {
 	
+		if (assertion != null) {
 			samlAsserionDao.deleteAssertionForUser(user);
 			
 			SamlAssertionEntity samlAssertionEntity = samlAsserionDao.createNew();
@@ -265,6 +266,7 @@ public class UserUpdater implements Serializable {
 			samlAssertionEntity.setAssertionData(samlHelper.prettyPrint(assertion));
 			samlAssertionEntity.setValidUntil(new Date(System.currentTimeMillis() + (4L * 60L * 60L * 1000L)));
 			samlAssertionEntity = samlAsserionDao.persist(samlAssertionEntity);
+		}
 		
 		Map<String, List<Object>> attributeMap = saml2AssertionService.extractAttributes(assertion);