If session doesn't exist, don't panic!

handlers/delete_instance.go

@@ -12,10 +12,15 @@ func DeleteInstance(rw http.ResponseWriter, req *http.Request) {
 	instanceName := vars["instanceName"]
 
 	s := core.SessionGet(sessionId)
+	if s != nil {
 		i := core.InstanceGet(s, instanceName)
 		err := core.InstanceDelete(s, i)
 		if err != nil {
 			rw.WriteHeader(http.StatusInternalServerError)
 			return
 		}
+	} else {
+		rw.WriteHeader(http.StatusNotFound)
+		return
+	}
 }