Fixed User login for non existing users (lookup().singleOrNull() isntead of .single())

spring-data-neo4j-examples/cineasts/src/main/java/org/neo4j/cineasts/repository/UserRepositoryImpl.java

@@ -31,7 +31,7 @@ public class UserRepositoryImpl implements CineastsUserDetailsService {
     }
 
     private User findByLogin(String login) {
-        return template.lookup(User.class,"login",login).to(User.class).single();
+        return template.lookup(User.class,"login",login).to(User.class).singleOrNull();
     }
 
     @Override