diff --git a/EduNetworkBuilder/NetworkDevice.cs b/EduNetworkBuilder/NetworkDevice.cs
index 8702491..b1b043f 100644
--- a/EduNetworkBuilder/NetworkDevice.cs
+++ b/EduNetworkBuilder/NetworkDevice.cs
@@ -464,6 +464,7 @@ namespace EduNetworkBuilder
                     if(Link != null)
                     {
                         NetworkDevice tmp = myNet.GetDeviceFromID(Link.Src);
+                        if (tmp == null) continue;
                         if (tmp.hostname != hostname) thelist.Add(tmp.hostname);
                          tmp = myNet.GetDeviceFromID(Link.Dst);
                         if (tmp.hostname != hostname) thelist.Add(tmp.hostname);