diff --git a/EduNetworkBuilder/IPAddress.cs b/EduNetworkBuilder/IPAddress.cs
index 001bf96..fb21f63 100644
--- a/EduNetworkBuilder/IPAddress.cs
+++ b/EduNetworkBuilder/IPAddress.cs
@@ -113,6 +113,7 @@ namespace EduNetworkBuilder
 
         public IPAddress(string ip)
         {
+            if (ip == null) ip = NB.ZeroIPString;
             myType = IPAddressType.ip;
             _ip = ip.ParseIp();
             var mySplitVal = ip.Split('/');